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

The Philippine military said the 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.

It also released another clip showing a white ship marked "China Coast Guard" crossing the bow of a grey vessel it identified as the Filipino 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 Filipino 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. 

The China Coast Guard said in a statement that it took "control measures according to law against Philippine vessels entering the waters adjacent to Ren'ai Reef", the Chinese name for the shoal.

It gave no details of what the measures entailed.

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.

Saturday's incident came just two days after another confrontation near Scarborough Shoal -- another contested South China Sea outcrop -- between the China Coast Guard and Filipino scientists who landed on two cays.

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

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

"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," it 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 "has been isolated from the resupply boat due to the irresponsible and provocative behaviour of the Chinese maritime forces", he added.