Chinese and Philippine coast guard vessels collided in the disputed South China Sea and four Filipino crew members were injured in a series of confrontations, as Southeast Asian leaders gathered for a summit where alarm over Beijing’s aggression at sea was expected to be raised.

The Chinese coast guard ships and accompanying vessels blocked the Philippine coast guard and supply vessels off the disputed Second Thomas Shoal and executed dangerous manoeuvres that caused two minor collisions between the Chinese ships and two of the Philippine vessels, Philippine officials said.

The BRP Sindangan of the Philippine coast guard sustained minor structural damage in the collision that happened shortly after dawn on Tuesday.

Over an hour later, another Chinese coast guard ship first blocked then collided with a supply boat the Philippine coast guard was escorting, the Philippine officials said.

The supply boat, manned by Filipino navy personnel, was later hit by water cannon blasts from two Chinese coast guard ships. Its windshield shattered, injuring at least four Filipino crew members, according to a statement from the Philippine government task force dealing with territorial disputes.

The task force said the actions by the Chinese was “another attempt to illegally impede or obstruct a routine resupply and rotation mission”.

“China’s latest unprovoked acts of coercion and dangerous manoeuvres” against Philippine ships en route to deliver supplies and fresh troops to the Philippine-occupied shoal “put the lives of our people at risk and caused actual injury to Filipinos,” it said.

A small Philippine marine and navy contingent has kept watch onboard a rusting warship, the BRP Sierra Madre, which has been marooned since the late 1990s in the shallows of the Second Thomas Shoal.

China also claims the shoal lying off the western Philippines and has surrounded the atoll with coast guard, navy and other ships to press its claims and prevent Filipino forces from delivering construction materials to fortify the Sierra Madre in a decades-long standoff.

The shoal has been the site of several tense skirmishes between Chinese and Philippine coast guard ships last year.

The Chinese coast guard said in a statement that “it took control measures in accordance with the law against Philippine ships that illegally intruded into the waters adjacent to Ren’ai Reef”, the name Beijing uses for Second Thomas Shoal.

A Chinese coast guard spokesperson said a Philippine ship deliberately rammed a Chinese coast guard vessel, causing a minor scratch.

The long-simmering territorial disputes in the South China Sea are expected to be discussed at a summit of leaders of the Association of Southeast Asian Nations and their Australian counterpart in Melbourne on Wednesday.

On Monday, Philippine President Ferdinand Marcos Jr said in the Australian city that his administration “will do whatever it takes” to manage any threat to his country’s territory but stressed that Manila would continue “to tread the path of dialogue and diplomacy” in resolving disputes with China.

The Philippines and Vietnam plan to raise their alarm over China’s increasingly aggressive actions in the disputed waters during the summit, a senior Southeast Asian diplomat told The Associated Press on condition of anonymity because of not being authorised to discuss the issue publicly.

Philippine security officials have accused the Chinese coast guard and suspected militia ships of blocking Philippine vessels and using water cannons and a military-grade laser that temporarily blinded some Filipino crew members in a series of high-seas confrontations last year.

The Chinese Embassy in Manila accused the Philippines of frequent provocative moves in the South China Sea and said China acted “in accordance with law to defend its own sovereignty, rights and interests”.

Washington strongly condemned the Chinese coast guard’s actions and its ambassador in Manila, MaryKay Carlson, said the US stands with the Philippines and proponents of international law.

Australia and Japan separately expressed their concern over China’s actions.

The confrontations have sparked fears of a larger conflict that could involve the US.

Chinese and Philippine officials met in Shanghai in January and agreed to take steps to lower tensions but their latest confrontation at sea underscores the difficulty of doing so.

The US has warned it is obligated to defend the Philippines, its oldest treaty ally in Asia, if Filipino forces, ships and aircraft come under an armed attack, including in the South China Sea.

China has warned the US to stop meddling in what it calls a purely Asian dispute.

Brunei, Malaysia Vietnam and Taiwan also have overlapping claims to the strategic waterway, a major global trade route which is also believed to be sitting atop rich undersea deposits of oil and gas.