Several nations have claims in the South China Sea, but China’s are by far the most extensive and controversial. The PRC uses its military to try to enforce sovereign rights and jurisdiction over features within the ‘Nine-Dash Line’, including the islands, rocks and atolls that make up the Paracel and Spratly islands. That’s despite a 2016 ruling by an international arbitration tribunal, which found that China’s Nine-Dash Line claim has no basis in international law.
The PRC also uses its military to deter other countries from operating in areas that it deems as ‘sensitive’. That includes using its military to deter other countries from approaching its contiguous zone—a region of sea that extends 12 nautical miles beyond a nation’s territorial waters. China’s military acts assertively when any foreign military operates close to its territory, especially major military installations.
Scroll below and click on the separate yellow headings in the text boxes below to move between analysis of excessive claims / sensitive areas and legal considerations.
China’s leaders claim that the islands, rocks and reefs of the South China Sea have belonged to China ‘since ancient times’. However, China’s so-called ancient claims are not even a century old. In 1936, the first U-shaped line in the South China Sea was drawn by Bai Meichu, a Chinese geographer. In 1947, the Republic of China drew up a map featuring Bai’s U-shaped line to depict its territorial claims. In 1949, the PRC adopted that claim following the victory of Chinese communist forces over the nationalists. Finally, in 1952, the U-shaped claim became the ‘Nine-Dash Line’ that we know today following an agreement between China and Vietnam over the Gulf of Tonkin.
A modern interpretation
The Nine-Dash Line is deliberately ambiguous. China has never publicly defined what the line represents but has passed domestic legislation to reinforce its claims. For example, in 1992, Beijing passed the ‘Law on the Territorial Waters and Their Contiguous Areas’, which provides details on China’s claims to four-fifths of the South China Sea.
In May 2009, China provided more detail on its claims when it issued a ‘note verbale’ to all UN members. The note included a map of the Nine-Dash Line and outlined that ‘China has indisputable sovereignty over all islands in the South China Sea’ and ‘enjoys sovereign rights and jurisdiction over all waters within the nine-dash line’.
The PRC’s sovereignty claims are also not ‘illegal’, as they have never been adjudicated on by an international court such as the International Court of Justice (a 2016 arbitration ruling provided a series of determinations, but not on sovereignty). However, China’s claims are ‘excessive’ and lack any basis in international law, such as UNCLOS.
A quick guide to UNCLOS
A brief history
Before UNCLOS, the oceans were largely governed by the 17th-century concept of the freedom of the seas. Coastal states had rights over a narrow band of territorial sea adjacent to their land, roughly equivalent to the distance that a cannonball could travel. However, across the 20th century, states began to extend their jurisdiction over the sea.
The UN held a series of meetings after World War II to standardise claims at sea. The first UN Conference on the Law of the Sea was held in Geneva in 1956 and resulted in four conventions. However, those conventions were soon deemed insufficient to meet the maritime challenges identified at the time. Another series of meetings was held in 1960 but didn’t reach any new agreements.
The UN convened the third UN Conference on the Law of the Sea in December 1973. After nine arduous years of negotiations, the conference adopted UNCLOS. UNCLOS was opened for signature on 10 December 1982 and entered into force on 14 November 1994. It’s been ratified by 170 parties (including China, Australia, Canada and the Philippines, but not the US).
Responsibilities under UNCLOS
UNCLOS sets guidelines to standardise states’ claims to maritime zones and provides mechanisms for settling disputes (but not sovereignty disputes). UNCLOS introduced important definitions relating to maritime zones and the rights of a state, such as:
Internal waters
All waters on the landward side of a country’s baselines, which connect the outermost land features. The state is free to set laws, regulate use, and use any resource. Vessels from foreign states can’t enter without diplomatic clearance, and merchant vessels must comply with port-state regulations.
Territorial waters
Out to 12 nautical miles (22 kilometres) from a country’s baseline. Vessels can conduct innocent passage without prior notification—defined as passage that’s continuous and expeditious and not prejudicial to the peace, good order and security of the state (meaning that foreign vessels can’t use force, exercise with weapons, collect information, launch aircraft and so on).
Contiguous zone
Beyond the 12-nautical-mile limit, there’s a further 12 nautical miles of contiguous zone, in which (if the zone is claimed) a state can continue to enforce laws in four specific areas: customs, taxation, immigration and pollution. A state can also commence hot pursuit in this area (if an infringement has occurred within the state’s territorial sea or internal waters) to prevent an infringement.
Exclusive Economic Zone (EEZ)
Extends out to a maximum of 200 nautical miles (370 kilometres) from a state’s baselines. Within this area, the coastal nation has sole exploitation rights over all marine resources, as well as the right to regulate marine scientific research and certain matters related to pollution control. Foreign nations have the freedom of navigation and overflight, and to lay submarine cables and pipelines (similar to the high seas).
The high seas
All parts of the sea that aren’t included in an EEZ, contiguous zone, territorial sea or internal waters of a state. They’re open to all states, and states enjoy freedoms including the freedom of navigation and freedom of overflight. No part of the high seas can be subject to claims of sovereignty.
China has occupied the Paracel Islands since 1974 after seizing them by force from South Vietnam and now maintains 20 outposts there. The outposts range in size from one or two buildings to bases with significant military infrastructure.
Woody Island is China’s main base in the Paracels. It has an airstrip, artificial harbour, naval facilities, surveillance radars and defences such as surface-to-air missiles and anti-ship cruise missiles.
China uses its military to try to enforce this extended claim—or straight baselines—around the Paracel Islands (it’s yet to do so around the Spratly Islands). Those enforcement attempts have led to unsafe interactions with foreign militaries (as outlined in the section detailing Unsafe military interactions).
How China contravenes UNCLOS
Despite being a signatory, China contravenes UNCLOS in a number of ways as outlined below:
Historical legacy
China claims to have owned the South China Sea ‘since ancient times’. However, UNCLOS doesn’t grant states the right to make such broad claims based on ‘historical legacy’.
Land dominates the sea
Under UNCLOS, maritime zones can only be generated from land over which a state has sovereignty (often described as the principle of ‘the land dominates the sea’). However, most of the features of the South China Sea don’t meet UNCLOS’s definition of land. There are simply not enough land features in the South China Sea to generate a zone as large as the Nine-Dash Line.
Agreement under international law
Maritime boundaries are agreed on the basis of international law. However, the ill-defined Nine-Dash Line lacks any basis under international law and is supported only through China’s domestic legislation and propaganda.
Straight baselines
By declaring and enforcing straight baselines around the Paracel Islands, China is illegitimately claiming the same rights as archipelagic states. However, that status is conferred only through the UN. Twenty-two states claim archipelagic status. China doesn’t meet the definition in Article 46, including the required ratio of water to land, so it can’t claim archipelagic status.
Regulating military access to territorial seas
China claims the right to deny innocent passage to warships in its territorial sea. Under Beijing’s domestic legislation, foreign military ships must obtain permission from the PRC Government to enter its territorial sea. However, UNCLOS is clear that any foreign vessel can conduct innocent passage through territorial waters.
Regulating military activities in EEZs
UNCLOS specifies that all vessels shall enjoy the rights of navigation and overflight in the EEZ of another country, provided they exercise due regard for the economic rights of the coastal states. However, in 1996, China declared that it shall ‘enjoy sovereign rights and jurisdiction’ over its EEZ. That includes the right to regulate the actions of foreign militaries. While most countries agree that international law protects the rights of foreign military vessels to move freely within an EEZ, several countries (including Brazil, India and Malaysia) agree with China’s interpretation that they enjoy sovereign rights and jurisdiction over their EEZs.
The Spratly Islands are spread out over a vast area of the South China Sea. China, Vietnam, Taiwan, Malaysia and the Philippines all have conflicting claims to the Spratlys, supported by garrisons on various features. Although Brunei doesn’t claim any territory, it has declared an EEZ that contains a Spratly reef.
The PRC first established a presence in the Spratlys in 1988. In late 2013, China began intensively building up artificial land on reefs and atolls within the Spratly Islands. It has now created over 13,000 square metres of land area through dredging and artificial-island building.
Beijing has developed seven outposts in the Spratlys, including three large garrisons with substantial military assets including runways, hangars, anti-air and anti-ship missiles, and communications facilities.
On 22 January 2013, the Philippines instituted arbitral proceedings against the PRC under UNCLOS. At the centre of the dispute was China’s Nine-Dash Line and increased efforts by Beijing to consolidate its position in the South China Sea via the harassment of foreign ships, resource extraction and the construction of artificial islands and military bases.
The Philippines asked the court to rule on:
whether China’s Nine-Dash Line claims were valid under UNCLOS
whether land features claimed by China could generate an EEZ and territorial seas
whether China had interfered with the Philippines’ right to exploit resources.
China repeatedly stated throughout the proceedings that ‘it will neither accept nor participate in the arbitration unilaterally initiated by the Philippines’ and instituted a program of media and diplomatic efforts to support its position. However, UNCLOS is clear that the ‘absence of a party or failure of a party to defend its case shall not constitute a bar to the proceedings’ (Annex VII).
The ruling
On 12 July 2016, the arbitral tribunal adjudicating the Philippines’ case against China in the South China Sea ruled overwhelmingly in favour of the Philippines. The court made no determination on sovereignty over disputed features; however, it found that China has no legal basis to claim ‘historic rights’ to areas falling within its Nine-Dash Line.
Key findings included the following:
China’s claims to historic rights and resources within its Nine-Dash Line have no legal basis.
‘China’s claims to historic rights, or other sovereign rights or jurisdiction, with respect to the maritime areas of the South China Sea encompassed by the relevant part of the “nine-dash line” are contrary to the Convention and without lawful effect’ (para 278).
China’s reclaimed features in the Spratly Islands aren’t islands capable of generating a 200-nautical-mile EEZ.
‘All of the high-tide features in the Spratly Islands are therefore legally rocks for purposes of Article 121(3) and do not generate entitlements to an exclusive economic zone or continental shelf’ (para 646).
China had violated the Philippines’ sovereign rights by interfering with the Philippines’ right to exploit resources.
‘China has … failed to exhibit due regard for the Philippines’ sovereign rights with respect to fisheries in its exclusive economic zone’ (para 757).
China’s reaction to the ruling was to reaffirm its territorial sovereignty and maritime rights in the South China Sea and to declare the ruling ‘null and void’, with ‘no binding force’.
Beyond the 12 nautical miles of territorial waters, there’s a further 12 nautical miles of sea that’s designated under UNCLOS as a state’s contiguous zone. A state has some but fewer rights within the contiguous zone (as outlined in A quick guide to UNCLOS) .
China has developed its own domestic legislation to govern its actions in the contiguous zone, outlined in its 1992 Law on the Territorial Sea and the Contiguous Zone. This law goes beyond the limited provisions outlined in UNCLOS, as it provides Chinese authorities with permissions to conduct enforcement against ‘any activity violating laws and regulations of the Republic of China’ (Article 14).
China’s problem with states enforcing sanctions against North Korea
Sanctions against North Korea
The UN Security Council (UNSC) has adopted nine major sanctions resolutions against North Korea in response to the country’s nuclear and missile activities. Despite those sanctions, North Korea has continued to develop its nuclear and missile capabilities, thanks in part due to a complex network of smuggling activities throughout North Asia. To combat that, the Pacific Security Maritime Exchange (PSMX)—an initiative involving Australia, Canada, France, Germany, Japan, New Zealand, South Korea, the UK and the US—was created. The group shares information and coordinates efforts to track, disrupt and deter North Korea’s illicit activities.
Operation Argos and Operation Neon
As do other countries in the PSMX, Canada and Australia use their military to enforce sanctions against North Korea. Australia’s military contribution is called Operation Argos, while Canada’s is known as Operation Neon.
Periodically, warships and aircraft from Canada and Australia patrol the East China Sea and Yellow Sea searching for smugglers and other actors violating UN sanctions against North Korea. North Korea and its friends attempt to evade those forces, using complex tactics. For example, a March 2024 report to the UNSC by the now-defunct Panel of Experts highlighted that smugglers are increasingly staying close to China’s coast to evade the forces looking for them.
As smuggling tactics evolve, law-enforcement agencies are also evolving their responses to that illegal activity. However, China is increasingly sensitive to the military forces of other countries operating close to its coastline. A May 2024 incident against Australia and unsafe intercepts against Canada in April and October 2023 are examples of that (details of those incidents are outlined under Unsafe military interactions) . On each occasion, Australia and Canada were clear that they were operating outside of China’s territorial waters and in accordance with international law to enforce UNSC sanctions against North Korea. Those are some of the very sanctions which the PRC, as a permanent member of the UNSC, helped to put in place. However, in all three incidents, China claimed that it had the right to intercept the foreign force as Canada and Australia’s actions ‘endangered China’s maritime and air security in the name of enforcing UNSC resolutions’.
The PLA Navy is divided into three fleets. The North Sea Fleet, headquartered in Qingdao, Shandong Province, is tasked with defending the coast off north and northeast China (the Bohai Gulf and Yellow Sea). The East Sea Fleet, headquartered in Ningbo, Zhejiang Province, conducts operations throughout the East China Sea and around Taiwan. Finally, the South Sea Fleet, headquartered in Zhanjiang, Guangdong Province, is responsible for operations in the South China Sea. China also maintains PLA Air Force capabilities as well as sensitive cyber, space and signals facilities at those locations.
Flight maps of US surveillance patrols demonstrate Washington’s continued interest in China’s military installations. As the Countries that challenge China’s excessive claims section outlines, other countries also operate within international waters and airspace close to those military bases, but not necessarily in a surveillance capacity.
Several unsafe interactions have taken place near China’s military bases, including the harassment of a Netherlands Navy vessel in June 2024. Beijing claimed that the Dutch were operating in waters off Shanghai, in close proximity to the Eastern Fleet headquarters. Similarly to the above examples with Australia and Canada, the Dutch stated that they were legally enforcing UN sanctions against North Korea.
As China becomes increasingly aggressive in trying to deter others from contesting its excessive claims and encroaching on its sensitive areas, it’s useful to look at how other countries treat China’s military, especially when the PLA is operating close to the territory of other countries. Three examples help to illustrate how other countries handle China’s approaches in their vicinity and demonstrate that China’s aggressive behaviour isn’t replicated by others:
In February and March 2025, a Chinese military task group consisting of a Jiangkai-class frigate, a Fuchi-class replenishment vessel and a Type 055 Renhai cruiser circumnavigated Australia in advance of national elections. The task group conducted provocative live-fire exercises, without notice, requiring commercial airliners to divert from their flight plans. The Australian and New Zealand militaries monitored the task group in a professional and safe manner throughout the circumnavigation.
In July 2024, the US intercepted two Russian and two Chinese bombers flying near Alaska, within America’s air defence identification zone. The intercept was reported in international media as being safe and legal.
In August 2024, Japan accused a Chinese surveillance aircraft of breaching its territorial airspace. Japan scrambled fighter jets in response to the incursion and issued ‘notifications and warnings’ to the Chinese aircraft, but no weapons or flares were used.
