Manila (AFP) - A Philippine-flagged tanker carrying 1.4 million litres of industrial fuel oil capsized and sank off Manila on Thursday, authorities said, as they raced to contain a spill.

The MT Terra Nova was heading for the central city of Iloilo when it capsized in Manila Bay, nearly seven kilometres (4.3 miles) off Limay municipality in Bataan province, near the capital, in the early hours.

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

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

An investigation into the cause of the incident was underway, but coast guard spokesman Rear Admiral Armando 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”, Balilo said in a statement.

At a briefing earlier Thursday, Balilo said authorities were “racing against time” to contain the spill and stop more fuel leaking.

He warned that if all the 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.

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

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

A search was underway for the missing crew member, but Bautista said strong winds and high waves were hampering response efforts.

Four of the crew were receiving medical treatment.

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 by a “strong current” in an easterly, northeasterly direction, the coast guard said in a report.

Marine environmental protection personnel have been mobilised to help contain the slick.

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

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.

In 2006, a tanker sank off the central island of Guimaras 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.