The foreign ministry in Manila said three Chinese crewmen had been rescued. It described the collision as an accident, caused by rough seas.

The incident took place on Sunday near a rocky outcrop known as Scarborough Shoal, which lies about 220km west of the main Philippines island of Luzon.

The Philippine navy says the patrol boat BRP Rizal chased three vessels carrying Chinese markings out of the area, and was about to send a boarding party onto one of them when the ships collided.

Rough conditions

Both countries have been staking their claim to disputed territory

"While the crew _ was preparing for boarding and search operations, the very rough sea conditions flung the Chinese vessel into BRP Rizal, causing the fishing junk to sink," its said in a statement.

There has been a tense confrontation between China and the Philippines over disputed territory in the South-China Sea since 1995 when the Filipinos discovered that China had occupied a disputed reef in the nearby Spratly Islands,

But in spite of the presence of warships from both countries in the disputed areas, this is the first such confrontation to result in the sinking of a ship.

The navy says a rescue operation began immediately after the collision.

Fuelling tensions

The BBC Correspondent in Manila, John McClean, says the incident is bound to exacerbate the dispute between the two countries over the Spratly Islands further south.

Announcing the incident, the Philippine Foreign Ministry reiterated Manila's position that Scarborough Shoal was Philippine territory.

There has so far been no response from the Chinese government although the Chinese embassy in Manila said it was "concerned about the incident".