The Philippine Coast Guard has deployed floating barriers and started to clean up an oil spill to prevent it from reaching the capital, Manila.
Authorities are racing to stop the oil spill from the 65-metre-long (213 feet) MT Terra Nova, which capsized on Thursday as monsoon rains battered large swathes of the country.
The leak appeared to be coming from the ship's engine, not its cargo tank, which was carrying close to 1.5 million litres of industrial fuel, officials said.
There are fears that the spill, which stretches out over several kilometres, could be the worst in the country's history if it is not contained.
Videos released by the coast guard show personnel siphoning oil from the affected waters with a bucket.
But officials are "preparing for the worst", said Rear Admiral Armand Balilo, the coast guard spokesman.
The area is popular with fishermen and there are fears the spill could affect both the fishing industry and marine life.
"We are talking about industrial fuel here... It will definitely affect the marine environment and could even reach us here in Manila," said Rear Adm Balilo.
Hernando Bacosa, an environmental sciences expert at the Mindanao State University,told the OceanNewsUK that the amount of oil the MT Terra Nova was carrying would warrant the issuance of the country's highest oil spill alert.
"Manila Bay is where the Port of Manila is, the biggest port in the Philippines and the center of trade and economic activity. This could possibly paralyse the capital and the neighbouring areas," he said.
Rear Adm Balilo estimated that it would take a week to drain oil from the ship, which capsized in an area with a depth of 34 metres (111 feet), according to initial assessments.
However, Mr Bacosa said the relatively shallow terrain could make it easier to siphon oil from the sea.
He compared it with an incident last year where an oil tanker sank off the coast of another Philippine province at a depth of almost 400 metres (1,312 feet) - stating that the deep waters made it more different to clean up the oil.
The MT Princess Empress had been carrying 800,000 litres of industrial fuel oil - coating beaches in black sludge when it spilt.
The monsoon rains, which were worsened by Typhoon Gaemi, have delayed the coast guard's response and caused widespread flooding across Metro Manila and its suburbs.
But the storm has since subsided as the typhoon moved across Taiwan's mountainous region and made landfall in the south-eastern Chinese province of Fujian.
The MT Terra Nova was one of two ships which sank in the region during the typhoon, with the second going down just off Taiwan's south-western coast.
It was heading for the central Philippine city of Iloilo when it sank, with 17 crew members on board.
One died, but 16 were rescued, officials said. Authorities are investigating whether bad weather was a factor.
The Philippine-flagged MT Terra Nova was found to have met regulations around travelling in heavy weather.
It was sailing towards the central Iloilo city at a speed of 0.1 nautical miles per hour, according to tracking provider VesselFinder.
Rear Adm Balilo said that no storm signals were issued when the ship set sail.
He added that crew members had secured its doors before jumping into the sea.
"They felt that the waves were really strong. The captain decided to return to shore, but it was difficult because they are sailing against the waves. They said the ship scooped up water until it eventually capsized," Rear Adm Balilo said.
Advocacy group Oceana has called on the Philippine government to assess the environmental impact of the oil spill, adding that "all those responsible for failing to prevent this tragedy - from concerned government agencies to private owners of the tanker - should be held accountable".
