COLOMBO: Environmentalists on Friday sued the Sri Lankan government and operators of a container ship loaded with chemicals and plastic that burned offshore for almost two weeks, as international experts prepared to deal with a possible oil spill.

The private Centre for Environment Justice (CEJ) petitioned the Supreme Court alleging that local authorities should have been able to prevent what they called the "worst marine disaster" in Sri Lanka's history. The Singapore-registered MV X-Press Pearl has been slowly sinking into the Indian Ocean since Wednesday after a fire that raged for 13 days within sight of the coast.

Tonnes of microplastic granules from the ship have swamped an 80-kilometre (50-mile) stretch of beach which has been declared off limits for residents. Fishing in the area was also banned.

The CEJ said government inaction was "against the concepts and principles of environmental law". A hearing is yet to be fixed. It said the crew knew of an acid leak on May 11, long before entering Sri Lankan waters, and local authorities should not have allowed the vessel in.

The legal challenge seeking unspecified damages came as foreign experts were deployed to help Sri Lanka contain a potential oil leak from the burnt-out wreckage.

Representatives from the International Tankers Owners Pollution Federation (ITOPF) and Oil Spill Response (OSR) were onshore monitoring the ship, the operators of the vessel, X-Press Feeders, said.

"They continue to coordinate with MEPA (the Marine Environment Protection Authority) and the Sri Lankan navy on an established plan to deal with any possible spill of oil and other pollutants," the Singaporean company said.

Its chief executive, Shmuel Yoskovitz, apologised to Sri Lanka for the disaster. "I'd like to express my deep regrets and apologies to the Sri Lankan people for the harm this incident has caused to the livelihood and to the environment of Sri Lanka," Yoskovitz told Channel News Asia.