The Philippines accused the China Coast Guard of blocking a Filipino supply vessel and damaging it with water cannon Saturday morning off a remote and contested South China Sea reef.

The Philippine military said the nearly hour-long attack occurred off Second Thomas Shoal, where Chinese ships have unleashed water cannon and collided with Filipino vessels in similar stand-offs in recent months.

The military released video clips that showed a white ship repeatedly dousing another vessel sailing alongside it with a water cannon. One clip showed two white ships simultaneously firing water at the same vessel.

It also released another clip showing a white ship marked "China Coast Guard" crossing the bow of a grey vessel it identified as the Philippine supply boat Unaizah May 4.

It said the videos were taken Saturday morning while the Unaizah May 4 was on its way to Ayungin Shoal -- the Filipino name for the outcrop garrisoned by a small unit of Philippine troops that is also claimed by Beijing.

"The UM4 supply boat sustained heavy damages at around 08:52 (am) due to the continued blasting of water cannons from the CCG vessels," the military said in a statement, without describing the nature of the damage or whether there were any casualties.

A Philippine coast guard escort vessel later reached the damaged boat "to provide assistance", the military said.

China Coast Guard spokesman Gan Yu said in a statement that the Philippine convoy "forcibly intruded into the area despite the Chinese side's repeated warnings and route controls", adding the Chinese carried out "control, obstruction and eviction in accordance with law".

"We sternly warn the Philippine side: those who play with fire will bring shame on themselves. The Chinese Coast Guard is ready at all times to resolutely safeguard our country's territorial sovereignty and maritime rights and interests," Gan added.

China claims almost the entire South China Sea, brushing off rival claims from countries including the Philippines and an international ruling that its assertion has no legal basis.

- 'Impeded and encircled' -

The latest confrontation came four days after visiting Secretary of State Antony Blinken said the United States stood by its "ironclad" commitments to defend longtime ally Manila against armed attack in the South China Sea.

Two days after Blinken's visit to Manila, the China Coast Guard also tried to drive away Filipino scientists who landed on two cays near Scarborough Shoal, another contested South China Sea outcrop.

The Unaizah May 4, which was also damaged in a China Coast Guard water cannon attack off Second Thomas Shoal earlier this month, had returned to the area on Saturday escorted by two Filipino coast guard vessels and two Philippine Navy ships, a Philippine military statement said.

The Philippine soldiers stationed on the shoal live on a derelict navy ship, the BRP Sierra Madre, and require frequent resupplies for food, water and other necessities.

"This particular mission was set up to ensure a full troop complement on board BRP Sierra Madre after one personnel needing serious medical attention was recently evacuated," the military added.

Four crew members had been hurt by broken glass during the previous water cannon attack on the Unaizah May 4.

Commodore Jay Tarriela, a Philippine coast guard spokesman for South China Sea issues, said in a separate statement that its escort vessel, the BRP Cabra, was "impeded and encircled" by three Chinese coast guard and other vessels early Saturday.

As a result, Cabra was "isolated from the resupply boat due to the irresponsible and provocative behaviour of the Chinese maritime forces", he added.