On Wednesday, experts from the Japanese and US coast guards joined Philippine disaster officials to assess the damage to dozens of communities in the provinces of Guimaras, Iloilo and Negros Occidental.

"While aerial surveys indicate that the leak has stopped, we have been gravely concerned about the possibility that the oil in the vessel will continue to be released," Petron Chairman Nicasio Alcantara said in a statement.

Petron, the largest oil refiner in the Southeast Asian country, hoped to recover the cargo of fuel before bringing the tanker to the surface, he said.

Coast guard and Petron officials have given conflicting statements about whether there are new leaks from the tanker, which is estimated to be 640 metres (2,100 feet) under water.

The Japanese salvage ship, which left Okinawa on Tuesday night, is equipped with state-of-the-art equipment that provides images of the ocean floor from a remotely operated vehicle.

"After we determine the tanker's exact location and condition, we can decide how best to remove the oil," Carlos Tan, Petron's health, safety and environment manager, told Reuters.

Philippine President Gloria Macapagal Arroyo ordered some 20 million pesos (US$390,000) to be given to local governments in the central Visayas region to provide relief to thousands of people affected by the spill.

The 998-tonne tanker, Solar 1, was carrying about 2 million litres of bunker oil. The initial spill of about 200,000 litres affected 20 coastal villages and a marine park in Guimaras.

The slick has since spread to 27 fishing villages in the towns of Concepcion and Ajuy in Iloilo, with officials saying it now threatens the islands of Negros, Cebu and Masbate.

Beyond the spill fouling beaches and the waters of the marine park, there are fears that the fuel could damage rich fishing grounds and the local tourism industry. Officials have warned residents not to eat anything from the sea but many, with few alternatives for food, have ignored the advice.

Petron said it was employing an average of 740 people per day in Guimaras, paying them 200 pesos each to clean the beaches and mangrove trees of the black sludge. (US$1= 51.4 pesos)