An environmental disaster off the coast of Sri Lanka is getting worse after a large container ship carrying chemicals and plastic that had caught fire is now sinking.

Sri Lankan authorities on Thursday said they are preparing for the worst-case scenario of a possible oil slick from the ship sinking off Colombo’s main harbour.

The Marine Environment Protection Authority readied oil dispersants, booms and skimmers in case of a leak from the MV X-Press Pearl, which has nearly 350 tonnes of oil in its fuel tanks.

The vessel, which burned for 13 days within sight of the island’s west coast, has already caused the country’s worst maritime environmental disaster, littering the beaches with huge volumes of plastic pollution.

But now that it is sinking, officials fear an even greater ecological crisis if the ship’s oil leaks into the Indian Ocean.

“One part of the vessel has hit the seabed and that has caused another plethora of headaches for all the authorities who can’t move it and know it is sinking. So, it’s almost inevitable and all they can do is get ready,” Global News Insight’s Minelle Fernandez said in her report from Colombo.

Navy spokesman Indika de Silva said there has been no oil leak from the ship yet. “But arrangements are in place to deal with a possible spill which is the worst-case scenario,” he said.

An Indian coastguard vessel already in the area has the equipment to deal with an oil slick before it could reach the beaches, according to the Sri Lankan navy, which has requested additional assistance.

The Singaporean operators of the MV X-Press Pearl said the vessel was continuing to slowly sink after efforts to tow it farther from the coast on Wednesday failed.

“X-Press Feeders … can confirm that the ship’s aft portion is sitting on the seabed at a depth of about 21 meters [69 feet], and the forward section is settling down slowly,” the company said in a statement on Thursday.

Sri Lanka’s navy said the bow of the vessel was still above the waterline as of Thursday morning.

“Even if the bow also hits the sea bed, still there will be a section of the upper deck and bridge sticking out of the water,” navy spokesperson Indika de Silva told the AFP news agency.

“Overall, it is a huge and mammoth task for the authorities and everybody’s just watching to see how bad things get,” said Fernandez.