The Philippines said China made dangerous moves and deployed a chopper during Manila’s research mission to South China Sea, the latest flare-up in lingering tensions between the two nations over disputed waters.

A China Coast Guard ship tried to prevent a Philippine fisheries bureau vessel from reaching sand bars off Manila-administered Thitu Island to check the status of marine life, Philippine Coast Guard spokesperson Commodore Jay Tarriela told a group of journalists who joined this week’s maritime mission.

China also deployed militia ships in the area as seen from Thitu by journalists including from Bloomberg News.

China’s coast guard said Filipinos on the ships ignored China’s warnings and its officers boarded Sandy Cay on Thursday to investigate and dealt with the situation in accordance with law, according to its WeChat account.

Tarriela disputed China’s statement, saying the Philippines was able to proceed with its research mission off Thitu Island. He also said China likely deployed the Navy chopper for surveillance.

Researchers saw dead corals and small species of fish that suggest environmental degradation at Sandy Cay, said marine biologist Jonathan Anticamara, who joined the mission.

The incident marks a new front in maritime encounters between Beijing and Manila as the two countries assert their overlapping South China Sea claims. The Philippines deployed its vessels off Thitu on Thursday to study for the first time corals, fish and other marine resources in the vicinity of Sandy Cay, where several Chinese ships had earlier been spotted.

Tensions between China and the Philippines have been escalating for months as Manila pushes back against a growing number of incursions around key features that both nations claim as their own.

Since coming to power in June 2022, President Ferdinand Marcos Jr. has taken a more assertive posture to the dispute compared to his predecessor, Rodrigo Duterte, while also leveraging close ties with the US in an effort to build a deterrence.

Marcos told Bloomberg News on Tuesday that the threat to his nation from China’s sweeping claims in the South China Sea is growing and that the Philippines “must do more to defend our territory.” Secretary of State Antony Blinken, on a visit to Manila this week, criticized China’s “provocative actions” in the contested waters as he reaffirmed the US security commitment to the Philippines.

The number of Chinese maritime militia vessels around key features across the South China Sea grew 35% last year with the help of more than 20 outposts in the Paracel and Spratly Islands, according to the Washington-based Asia Maritime Transparency Initiative. China is known to utilize a so-called backbone fleet to patrol or swarm such areas including earlier this month around Whitsun Reef, according to observers.

The Philippines’ coast guard recently built a new surveillance base on Thitu Island — complete with radar, satellite communication, coastal cameras and automatic identification capability — to boost its capacity to monitor movements of Chinese ships.

Stretching from China in the north to Indonesia in the south, the South China Sea encompasses 1.4 million square miles (3.6 million square kilometers), making it bigger than the Mediterranean Sea. It’s a thriving fishing zone — yielding some 10% of the global catch — and holds promising oil and natural gas reserves.

A vast amount of trade transits through its waters. In 2016, that amounted to some $3 trillion, including more than 30% of the global maritime crude oil trade.

Chinese coast guard ships attempt to block Philippine vessels carrying scientists in South China Sea

In this photo provided by the Philippine Coast Guard, a Chinese coast guard ship, top, tries to block a Philippine government vessel at the disputed South China Sea on Thursday March 21, 2024. Chinese coast guard ships, backed by a military helicopter, tried to dangerously block but failed to stop two Philippine government vessels carrying scientists from reaching two barren sandbars called Sandy Cay in the disputed South China Sea, Philippine officials said Friday.

Chinese coast guard ships backed by a military helicopter attempted unsuccessfully to block two Philippine government vessels carrying scientists from reaching two sandbars in the disputed South China Sea, Philippine officials said Friday.

Chinese coast guard personnel blew the horn on one of their ships for half an hour and repeatedly transmitted radio warnings during the confrontation Thursday, but the Filipino scientists managed to complete their four-hour marine and biodiversity research at the barren sandbars called Sandy Cay, the officials said.

The Chinese coast guard gave a different account of the faceoff. A spokesperson, Gan Yu, said in a statement that its law enforcement officers “boarded” the sandbars, which Beijing calls Tiexian Reef, and dealt with what it called “illegal activities” by 34 Philippine personnel who “ignored China’s warnings and dissuasion.”

“That’s another lie coming from the Chinese coast guard,” Philippine coast guard Commodore Jay Tarriela said at a news conference on Friday. “For four hours, our marine scientists were able to continue their research.”

Journalists who were invited to join the research mission witnessed the incident, Tarriela said.

It was the latest flareup in increasingly tense territorial disputes that are seen as a potential Asian flashpoint that might bring China and the United States into a conflict if they degenerate into a major armed confrontation.

China, the Philippines, Vietnam, Malaysia, Taiwan and Brunei have overlapping territorial claims that have erupted from time to time into brief confrontations in the South China Sea.

Hostilities between China and the Philippines, however, have worsened since last year, resulting in minor collisions at sea and injuries to a few Filipino crewmen, sparking a war of words.

Washington has no territorial claims in the strategic waterway but has questioned China’s claim to virtually the entire seaway. The United States has repeatedly warned that it’s obligated to defend the Philippines, its oldest treaty ally in Asia, if Filipino forces, ships and aircraft come under an armed attack.

During the Chinese coast guard’s maneuvers, one of its ships crossed the bow of the Philippine fisheries vessel BRP Datu Sanday at a distance of 100 meters (328 feet), Tarriela said. At least 13 suspected Chinese militia vessels tried to help form a blockade, he said.

Two of the three small sandbars where the Filipino scientists carried out a survey are located between Philippine-occupied Thitu island and Subi, a disputed reef that China transformed into an island base with a military-grade runway, seaports and a number of buildings with communications facilities.

In 2017, Chinese officials accused the Philippine military of attempting to build a structure on one of the sandbars, and deployed Chinese coast guard and suspected militia ships to keep watch on Sandy Cay.

China coast guard says it took measures against Philippine vessels in South China Sea

China's coast guard said it had taken control measures against Philippine vessels in disputed waters of the South China Sea on Saturday, while the Philippine coast guard decried the moves as "irresponsible and provocative".

The incident occurred in the Second Thomas Shoal and Spratly Islands waters, according to the Chinese coast guard. The shoal is home to a small number of Filipino troops stationed on a warship that Manila grounded there in 1999 to reinforce its sovereignty claims.

China claims almost the entire South China Sea, including the Second Thomas Shoal, and has deployed vessels to patrol the disputed atoll. A 2016 ruling by the Permanent Court of Arbitration found that China's sweeping claims have no legal basis.

A Philippine civilian boat was hired to resupply the troops this week, and was escorted by two Philippine navy ships and two Philippine coast guard vessels, according to a statement from the Philippine armed forces on Saturday.

A Philippine coast guard vessel was "impeded" and "encircled" by one Chinese coast guard vessel and two Chinese maritime militia vessels, the Philippine Coast Guard said in a separate statement.

As a result, the Philippine coast guard vessel was "isolated" from the resupply boat by the "irresponsible and provocative behaviour" of the Chinese maritime forces, the Philippine coast guard said.

The Chinese side showed a "disregard" for the Convention on the International Regulations for Preventing Collisions at Sea (COLREGS).