Authorities in Sri Lanka were trying to head off a potential environmental disaster Thursday as a fire-damaged container ship that had been carrying chemicals was sinking off of the country’s main port.

The Singapore-flagged MV X-Press Pearl started sinking Wednesday, a day after authorities extinguished fire that raged on the vessel for 12 days. Efforts to tow the ship into deeper waters away from the port in Colombo failed after the ship’s stern became submerged and rested on the seabed.

The ship’s operators X-Press Feeders have said the fire destroyed most of the ship’s cargo, which included 25 tons of nitric acid and other chemicals. But there are fears that remaining chemicals as well as hundreds of tons of oil from the vessel’s fuel tanks could leak into the sea if it sinks.