One crew member of the MT Terra Nova was killed when the tanker capsized in Manila Bay, nearly seven kilometres (4.3 miles) off Limay municipality in Bataan province, as it sailed to the central city of Iloilo.

The vessel went down in rough seas as heavy rains fuelled by Typhoon Gaemi and the seasonal monsoon lashed Manila and surrounding regions in recent days.

An oil slick stretching several kilometres has been detected and the Philippine Coast Guard was preparing to apply dispersants and deploy floating barriers to contain the spill.

Coast guard spokesman Rear Admiral Armando Balilo told a briefing earlier on Thursday authorities were "racing against time" to contain the spill and stop more fuel leaking.

It appeared so far that diesel fuel used to power the tanker was leaking into the sea but not the industrial fuel oil cargo, Balilo said. 

He warned that if all the industrial fuel oil in the tanker were to leak, it would be the biggest spill in Philippine history.

"There is a big danger that Manila will be affected, even the shoreline of Manila, if the fuel will leak, because it is within Manila Bay," Balilo said.

Transport Secretary Jaime Bautista said 16 of the 17 crew had been rescued from the stricken vessel.

The body of a missing crew member was found in the afternoon after rescuers spent hours searching the choppy waters, the coast guard said.  

An investigation into the cause of the incident was underway but Balilo said the vessel had not broken rules on heavy weather sailing.

A Public Storm Warning Signal had not been raised when the MT Terra Nova departed Limay and "therefore did not violate rules and regulations", he said in a statement.

Thousands of fishermen and tour operators are dependent on the waters for their livelihoods.

A photo released by the coast guard showed the MT Terra Nova almost entirely submerged in rough seas. 

It has since sunk 34 metres below the waves, which Balilo said was "considerably shallow" and meant siphoning the oil out of the tanker "can be done quickly".

Coast guard Commandant Admiral Ronnie Gavan said they had set a target of seven days to complete the siphoning.

Investigation ordered 

An oil slick stretching about 3.7 kilometres was being carried northeast by a "strong current", the coast guard said.

Marine environmental protection personnel have been mobilised to help contain the slick. The coast guard said it was also working with some oil spill response organisations and oil companies, including Petron, had offered to help.

"It will definitely affect the marine environment," Balilo said, describing the amount of oil on the ship as "enormous".

The leader of a local fishing group said the spill was "really alarming" and urged authorities to contain it as quickly as possible.

"The livelihood of our fishermen is dependent on the waters. They don't have any alternative," Pando Hicap, chairman of the Pamalakaya fishing group, told AFP.

One of the worst oil spills in the Philippines was in February 2023, when a tanker carrying 800,000 litres of industrial fuel oil sank off the central island of Mindoro.

Diesel fuel and thick oil from that vessel contaminated the waters and beaches along the coast of Oriental Mindoro province, devastating the fishing and tourism industries.  

The oil dispersed over hundreds of kilometres of waters famed for having some of the most diverse marine life in the world.

Thousands of fishermen were ordered to stay ashore and swimming was banned.

A tanker sank off the central island of Guimaras in 2006, spilling tens of thousands of gallons of oil that destroyed a marine reserve, ruined local fishing grounds and covered stretches of coastline in black sludge.