The Philippines says its main naval vessel is engaged in a stand-off with Chinese surveillance ships at a disputed South China Sea shoal.
The Philippines said its warship tried to arrest Chinese fishermen anchored at the Scarborough Shoal, but was blocked by the two surveillance boats.
Both countries dispute the ownership of the shoal, which lies off the Philippines' northwestern coast.
The Philippine government said it would "assert sovereignty" over the area.
A statement from the county's Ministry of Foreign Affairs said the naval vessel, the Gregorio Del Pilar, found eight Chinese fishing vessels at the shoal when it was patrolling the area on Sunday.
Two Chinese surveillance ships then apparently arrived in the area on Tuesday, placing themselves between the warship and the fishing vessels.
According to French news agency AFP, Philippine Foreign Affairs Secretary Albert del Rosario contacted China's ambassador to the Philippines, Ma Keqing, to emphasise that the Scarborough Shoal area was "an integral part of Philippine territory".
He is said to be seeking a diplomatic solution to the situation.