"Sad to note that the large oil spill is now wreaking havoc to the fishing grounds, beautiful diving spots, marine sanctuaries and other sensitive coastal areas in Guimaras island," the Coast Guard said in a statement.

Vice-Admiral Arthur Gosingan, the head of the Coast Guard, told Reuters that the bunker oil, covering a stretch of about 19.5 nautical miles, could take up to three years to clean.

Clumps of the greasy liquid, smelling of newly laid asphalt, stained the beach in the fishing village of Lapaz. Residents placed nets along the shore to obstruct the slick but large waves washed them away.

The Taklong island national marine reserve, located on the southern tip of Guimaras island, was one of the areas hit after a tanker, chartered by the Philippines' largest refiner Petron, sank on Friday with 2 million litres of bunker oil.

The marine reserve is a feeding and breeding ground for fish and other species. Scientists recorded 29 genera of hard coral in the area, 144 species of fish, 7 species of seagrasses and 3 species of mangroves.

Gosingan said the Coast Guard would ask their counterparts in Indonesia and Japan for technical help on stopping the spread of the oil.

The Philippines would also seek help to salvage the tanker, Solar 1, which sank while en route to a power plant on the southern island of Mindanao. Eighteen crew were rescued and 2 remain missing.

Environmental group Greenpeace said the Philippines must hold Petron and its partners accountable for the damage to coastal and marine ecosystems.