As two Philippine vessels meet on the high seas to transfer a sick Filipino soldier, China Coast Guard boats shadow, block and bump them, according to video released by the Philippine Coast Guard on Friday.

The incident happened last month during the medical evacuation of a soldier who was stationed on a grounded Philippine Navy vessel, the BRP Sierra Madre, on Second Thomas Shoal in the disputed South China Sea.

The Philippine Coast Guard said they had deployed a boat on May 19 to retrieve the soldier from a Philippine Navy speedboat, and had informed the China Coast Guard of the "humanitarian nature" of their mission.

In a series of videos released by the Philippine Coast Guard, a Chinese-flagged inflatable speedboat is seen bumping into the two stationary Philippine vessels as they prepare to transfer the patient.

Other boats -- identified by the Philippines as belonging to the China Coast Guard -- are also seen shadowing and blocking the path of the Philippine Coast Guard boat.

The Chinese boats "engaged in dangerous manoeuvres" and "intentionally rammed" the Philippine Navy vessel, Philippine Coast Guard spokesman for the West Philippine Sea Jay Tarriela said in a statement.

"The barbaric and inhumane behaviour displayed by the China Coast Guard has no place in our society," Tarriela said.

"What should have been a simple medical evacuation operation was subjected to harassment," he said.

"Their actions clearly demonstrated their intention to prevent the sick personnel from receiving the proper medical attention he urgently needed."

China's foreign ministry said in response to the accusation it could "allow" the Philippines to deliver "necessary supplies" and evacuate personnel from the Sierra Madre if Beijing were notified in advance.

"However, the Philippines should not use this as an excuse to ship construction materials to the deliberately grounded warship in an attempt to permanently occupy the Ren'ai Reef," spokeswoman Mao Ning said, using China's name for Second Thomas Shoal.

Beijing claims almost the entire waterway and there has been a series of confrontations involving Chinese and Philippine vessels near contested reefs, often around Second Thomas Shoal in the Spratly Islands.

Second Thomas Shoal is about 200 kilometres (120 miles) from the western Philippine island of Palawan and more than 1,000 kilometres from China's nearest major landmass, Hainan island.

The Filipino soldier was eventually loaded onto the Philippine Coast Guard boat and taken to Palawan, where he received hospital treatment.

The Philippines did not provide details of the soldier's medical condition.

- Rival claims -

Other videos released by the Philippines on Friday showed China Coast Guard vessels shadowing three Philippine Coast Guard speedboats carrying marine scientists from the University of the Philippines this week.

The scientists were examining crushed coral found at two sandbars in Sabina Shoal, also in the Spratlys.

One video showed a Chinese inflatable speedboat nudging one of the Philippine boats.

The Philippine military said Tuesday that Chinese boats had illegally "seized" food and medicine that was airdropped on May 19 to troops garrisoned on the Sierra Madre.

It was the first time supplies had been seized, it said.

Chinese personnel on board the boats later dumped the items in the water, said Commodore Roy Vincent Trinidad, Philippine Navy spokesman for the West Philippine Sea.

China brushes off rival claims to the South China Sea from other countries, including the Philippines, and ignores an international ruling that its claims have no legal basis.

To assert its stance, Beijing deploys coast guard and other boats to patrol the waters and has turned several reefs into artificial islands that it has militarised.

China Coast Guard vessels have used water cannon against Philippine boats multiple times in the contested waters, where there have also been collisions that injured several Filipino troops.

Philippine President Ferdinand Marcos said in a defiant speech at a security forum in Singapore last week he would not yield to Chinese pressure.