This is the moment China Coast Guard ships blasted water cannons on a Philippine boat leaving it 'heavily damaged'.

Footage shows two Chinese vessels bombarding the Philippine Coast Guard's (PCG) Unaizah May 4 ship while it was on a resupply mission in a contested part of the South China Sea on March 23.

The high-pressure streams were seen scouring off part of the ship's roof.

Officials said several people were injured, though they have not clarified the number.

Another PCG vessel, the BRP Cabra, approached the Unaizah May 4 to provide assistance.

The Unaizah May 4 is the same Philippine vessel that was blasted with water cannons by the CCG earlier this month, injuring four Filipino crew members.

It was bringing supplies to Filipino soldiers at the military outpost BRP Sierra Madre in the Second Thomas Shoal when the attack occurred.

The China Coast Guard said in a statement that it took 'regulatory actions' against the Philippine vessels entering the area 'illegally'.

China currently lays claim over almost the entire South China Sea, one of the world's busiest sea lanes. But a United Nations-backed tribunal in 2016 deemed its claims groundless.