Coast guard chief Arthur Gosingan said the tanker, carrying around 1.8 million litres of oil, was seen lying in an upright position under about 640 metres (2,100 feet) of water off the island of Guimaras.

"A crack was seen on its right side, but no fresh leaks were observed," Gosingan told government-run PTV 4 television.

The Japanese ship, Shinsei Maru, arrived in Iloilo, near Guimarasto, on Wednesday to assess the condition of the 998-tonne tanker.

It will take experts two days to make a recommendation on whether to siphon off the oil, raise the ship or entomb it.

Greenpeace says the remaining fuel in the tanker is an ecological timebomb.

If the Japanese experts, who arrived from Okinawa late on Wednesday, recommend raising the Solar 1 another salvage vessel has to be hired.

"The Shinsei Maru will only carry the remote operated vehicle that will probe the area where Solar 1 sank. It does not have the equipment to actually salvage the vessel," said a spokeswoman for refiner Petron, which chartered the Solar 1.

Petron, which is 40 percent owned each by the Philippine government and Saudi Aramco, has promised to do everything "humanly possible" to help affected villagers and clean smeared beaches and mangroves in Guimaras and Iloilo provinces.

It has hired about 1,000 locals, paying them as much as 300 pesos each day (US$5.90), to clean the beaches and mangroves of the oil slick.