Manila: The Philippines has relaunched an old US Coast Guard cutter as its biggest and most modern warship to guard potentially oil-rich waters that are at the center of a dispute with China.

President Benigno Aquino III witnessed the commissioning of the 3,390-ton Philippine navy frigate BRP Gregorio del Pilar in an austere ceremony on Wednesday that he said symbolised his country's struggle to modernise its underfunded military despite many obstacles.

Aquino said the Philippines cannot guard its territorial waters and islands "with dilapidated vessels and old and faulty equipment."

The newly repainted warship can carry a surveillance helicopter and is mounted with anti-aircraft guns. The navy says it will be deployed near contested waters in the South China Sea.