A Philippine fuel tanker partially sank in the country's waters Tuesday, authorities said, as they tried to contain a diesel spill stretching several kilometers.

The Princess Empress was carrying 800,000 liters of industrial fuel oil from Bataan province, near the capital Manila, to the central province of Iloilo when its engine overheated, the Philippine Coast Guard said.

An initial investigation showed the "distressed" vessel drifted towards waters off Balingawan Point on Mindoro island "due to rough sea conditions until it became half-submerged".

The coast guard said it was monitoring a spill of diesel fuel, which had been powering the vessel, but had not found in the sea any industrial fuel oil from the ship's cargo.

Another vessel rescued the 20 crew members on board. The coast guard said they were in "good physical condition."

In a separate update, the coast guard said the spill detected near the stricken vessel was five kilometers long and 500 meters wide.

An oil spill boom would be installed to control the spillage, it said.