The Philippines said China made dangerous moves and deployed a chopper during Manila’s research mission to the 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”. US Secretary of State Antony Blinken, on a visit to Manila this week, criticised 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 utilise 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 km), 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 US$3 trillion , including more than 30% of the global maritime crude oil trade.

  - Bloomberg