A halted resupply run by Philippines, a grounded warship and the decades-old dispute over the South China Sea

The Philippines said on September 25 that Chinese coast guard and navy vessels had "obstructed" a resupply mission the previous day to its troops stationed aboard a grounded warship at the Second Thomas Shoal, a reef about 195km west of the island of Palawan.

The Philippine military said three Chinese navy ships, including two missile boats, and five coast guard vessels were involved. The mission was called off without delivering supplies or rotating the troops.

The Philippine foreign ministry has said a 2024 arrangement on these missions helped prevent confrontations between the two sides. In July, Manila had accused China's coast guard of striking a Philippine navy staff member with a wooden baton during a separate encounter near the shoal.

China responded, with its coast guard saying that the Philippines had breached its commitments and sent the supply vessel despite its warnings.

On September 27, Lee Lipton, the US ambassador to the Philippines, said Washington "strongly condemns the use of dangerous blocking and other irresponsible manoeuvres" by China's coast guard and navy. He called on both to "cease the use of escalatory tactics that threaten the freedom of navigation and a free and open Indo-Pacific".

Hours later, the Chinese embassy in Manila condemned what it called the US embassy's "disregard for right and wrong" and urged Washington to "stop fanning the flames".

The same day, China's military held joint naval and air drills around the Scarborough Shoal, a reef about 220km west of the island of Luzon that China has controlled since a 2012 standoff with Manila.

The incidents are the latest in a series of confrontations in a sea where China and several Southeast Asian countries claim overlapping stretches of water and hundreds of small islands and reefs.

The shoal, which the Philippines calls Ayungin and China calls Ren'ai Jiao, is in the Spratly Islands.

In 1999, a World War II-era navy ship, the BRP Sierra Madre, was deliberately run aground on the reef. Since then, a small contingent of Philippine navy personnel and marines has lived aboard, depending on regular boat runs for food and other supplies.

China claims the shoal, and its coast guard has repeatedly tried to block those runs. In June 2024, Chinese coast guard personnel rammed and boarded Philippine navy boats during one such mission, and a Filipino sailor lost a thumb. A month later, the two countries reached a provisional understanding on resupply missions. Manila says the understanding does not require it to seek China's permission.

The South China Sea is an arm of the western Pacific Ocean, bordered by China and Taiwan to the north, the Philippines to the east, Malaysia, Brunei and Indonesia to the south, and Vietnam to the west.

China claims most of it through the 'nine-dash line', a U-shaped boundary that encloses nearly 90% of the sea. That is about 2 million sq km of water but only about 13 sq km of land, not counting Taiwan and the Pratas Islands. The line began as an eleven-dash line on a map published in 1947 by the Republic of China government, two years before the founding of the People's Republic of China. After the Communists came to power, Beijing dropped the two dashes in the Gulf of Tonkin.

Taiwan, Vietnam, Malaysia, Brunei, Indonesia and the Philippines all have claims that overlap with China's, covering more than 200 small islands, reefs and shoals or the waters around them. Indonesia says it is not a party to the territorial dispute, and it objects to the nine-dash line because it takes in waters around the Indonesian-ruled Natuna Islands.

In May 2009, China sent a note to the UN secretary-general objecting to a joint submission by Vietnam and Malaysia to the UN Commission on the Limits of the Continental Shelf. It attached a map of the nine-dash line. The note asserted China's "indisputable sovereignty over the islands in the South China Sea and the adjacent waters".

Beyond that assertion, Beijing has not published coordinates for the line or said what it covers.

Analysts have long asked whether China claims all the water inside the dashes, or only the islands and the resources around them. Under the UN Convention on the Law of the Sea (Unclos), coastal states must deposit with the UN secretary-general charts or lists of geographical coordinates for their baselines and the outer limits of their maritime zones, and must publicise them. Without those, other countries cannot measure China's claim against the treaty.

China has pressed its claims harder since Xi Jinping became president in 2013. It has built artificial islands on reefs, challenged foreign naval vessels, military aircraft and fishing boats in the area, and asserted its right to explore and extract oil and gas in waters other countries claim.

According to the Asia Maritime Transparency Initiative at the Center for Strategic and International Studies (CSIS), a Washington-based think-tank, satellite imagery shows China has built military installations, ports and airstrips on the features it holds. It has 20 outposts in the Paracel Islands, which it has fully controlled since a 1974 battle with South Vietnam, and seven in the Spratly Islands, where Vietnam has the most outposts of any claimant.

In January 2013, the Philippines challenged China's claims under Unclos. In July 2016, an arbitral tribunal constituted under the convention and administered by the Permanent Court of Arbitration (PCA) in The Hague ruled that China's claims to historic rights within the nine-dash line had no legal basis. The tribunal also found that the Second Thomas Shoal is a low-tide elevation, which cannot be claimed as territory, and that it is part of the Philippines' exclusive economic zone.

China's foreign ministry declared the award "null and void" with "no binding force".

Beijing views control of the sea as essential to its security. About 80% of China's oil imports pass through the Strait of Malacca, between Malaysia and Indonesia, before entering the South China Sea. In 2003, then president Hu Jintao warned of what he called the "Malacca dilemma", the risk that a hostile power controlling the strait could cut off China's energy supply. As the US draws closer to countries around the sea, Beijing sees control of its waters as part of the answer.

Analysts also see the sea as a buffer in the event of a wider war in the region, including one over Taiwan, which Beijing claims as its territory.

The South China Sea carries an estimated third of global shipping, according to the UN Conference on Trade and Development (Unctad). The US Energy Information Administration estimated in 2013 that it holds about 11 billion barrels of oil and 190 trillion cubic feet of natural gas in proved and probable reserves. Most of these lie in uncontested waters near the coastlines, not around the disputed islands.

It is also a major fishing ground and important to food security in the countries around it.

These stakes drive the other claimants too, and could explain Washington's growing involvement. The Joe Biden administration's 2022 Indo-Pacific strategy pledged to "build support for rules-based approaches to the maritime domain, including in the South China Sea and the East China Sea".

In May, senators Tammy Duckworth, a Democrat, and John Curtis, a Republican, introduced the South China Sea Strategy Act of 2026 in the US Senate. It would require the secretary of state to submit, within 180 days, a strategy for US diplomatic engagement in the South China Sea, setting out Washington's goals and naming the office responsible for each. The version approved by the Senate Foreign Relations Committee brings Taiwan into the regional engagements the strategy must plan for. It also adds a clause stating that nothing in the bill "may be construed as a change to the One China Policy of the United States, which is guided by the Taiwan Relations Act..., the three United States-People's Republic of China Joint Communiques, and the Six Assurances".

The committee approved the bill in June. It has since been placed on the Senate's legislative calendar, which makes it eligible for debate on the floor.

Wall Street Journal: China aggressively patrols disputed waters. Now the US Coast Guard is moving in

In April 2022, the external affairs ministry told the Lok Sabha that, according to information available with it, over 55% of India's trade passes through the South China Sea and the Malacca Straits.

India's public position on the dispute has shifted in recent years. In June 2023, a year of frequent clashes between Manila and Beijing at sea, a joint statement issued after external affairs minister S Jaishankar met his Philippine counterpart Enrique Manalo underlined the need to abide by international law, including the 2016 arbitral award. In March 2024, Jaishankar said in Manila: "I take this opportunity to firmly reiterate India's support to the Philippines for upholding its national sovereignty."

In an April 2024 essay for the Observer Research Foundation, a New Delhi think tank, its vice-president Harsh V Pant and associate fellow Pratnashree Basu said both statements were "part of an evolving approach that signals a departure from India's earlier more cautionary and neutral position vis-à-vis the South China Sea". They wrote that the shift could not be separated from India's "complex relationship" with China, and that New Delhi's position reflected its "broader strategic and economic aspirations on the global stage".

In July 2025, after a meeting of foreign ministers of the Quadrilateral Security Dialogue (Quad) in Washington, Jaishankar told reporters that ensuring the South China Sea "stays calm and free of conflict" is "a common priority" for the group's four members, India, the US, Japan and Australia.

The joint statement issued after the meeting did not name China, but said the Quad opposes "any unilateral actions that seek to change the status quo by force or coercion".

It went on: "We express our serious concerns regarding dangerous and provocative actions, including interference with offshore resource development, the repeated obstruction of the freedoms of navigation and overflight, and the dangerous maneuvers by military aircraft and coast guard and maritime militia vessels, especially the unsafe use of water cannons and ramming or blocking actions in the South China Sea."

On September 29, addressing the Indian Navy's Commanders' Conference in New Delhi, defence minister Rajnath Singh said the presence of Indian warships extended to the South China Sea, the Mediterranean and the Atlantic. "The Indian Navy serves as a strategic anchor in the vision of 'Viksit Bharat 2047'. Beyond merely guarding maritime boundaries, our Navy strengthens economic protection, regional stability, and power projection," he said. He added that India imports nearly 85 to 90% of its crude oil and about half its natural gas by sea, so "the security of sea lanes is directly connected with the country's economy, energy supplies and defence preparedness".