The Philippines has sought help from Japan and the United States, authorities said Friday, as they struggle to contain and clean up an oil spill 10 days after a tanker sank.

The Princess Empress was carrying 800,000 litres (210,000 gallons) of industrial fuel oil when it went down in rough seas off the central island of Mindoro, south of the capital Manila.

The vessel is believed to be about 400 metres (1,300 feet) below the waves, but Philippine authorities have said the country does not have the capability to reach the wreckage and remove the oil.

Japan has sent coast guard personnel to Manila to support the investigation into the spill and "guide the ongoing oil removal and control activities", the Philippine Coast Guard said Friday.

Manila had also requested assistance from the United States, coast guard spokesman Armando Balilo told AFP.

He did not elaborate on the type of help sought, and the US embassy did not immediately comment.

Diesel fuel and thick oil from the tanker have contaminated the waters and beaches of nine municipalities along the coast of Oriental Mindoro province, known for its rich marine life.

More than 2,500 hectares (6,200 acres) of coral reefs, mangroves and seaweed could be affected by the spill, the environment ministry said previously.

It is not known how much diesel and oil have leaked into the water.

The Philippine Coast Guard said Friday it had found oil as far away as Casian Island, off the north coast of the western island of Palawan.

That is about 350 kilometres (220 miles) southwest of where the tanker sank.

Dozens of people have fallen ill in Oriental Mindoro after oil washed up on their shores, the provincial government said earlier this week.

Residents and coast guard personnel have been removing oil-coated seaweed and other debris from affected beaches.

An oil spill boom was deployed on Wednesday after rough seas hampered earlier efforts to contain the slick

Thousands of fishermen have been ordered to stay on shore until they can fish safely, and swimming is also banned.