Foreign experts have been deployed to help Sri Lanka contain a potential oil leak from a burnt-out container ship partially sunk off Colombo, the ship's operator said Friday.

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

"They continue to coordinate with MEPA (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 company said.

Its chief executive, Shmuel Yoskovitz, apologised to Sri Lanka for the disaster, which saw the ship burn for 13 days and inundated the island's beaches with huge amounts of plastic pellets.

"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.

With the ship's stern now on the sea bed and the bow slowly sinking, environmentalists fear an oil leak could cause even greater degradation to marine life.

Choppy seas and poor visibility prevented navy divers from checking the hull for a second day Friday, Sri Lanka navy spokesperson Indika de Silva told AFP.

He said a team reached the sinking vessel and made a cursory inspection on Thursday, but could not carry out their mission because of poor visibility.

Meanwhile, the MEPA has placed oil dispersants and skimmers should the vessel leak its 350 tonnes of fuel oil on board.

An Indian coastguard vessel in the area has equipment to deal with any oil slick, according to the Sri Lankan navy, which has requested assistance with the operation.

Sri Lanka's Harbour Master Nirmal Silva said Thursday that no oil had leaked so far.

"Looking at the way the ship burnt, expert opinion is that bunker oil may have burnt out, but we are preparing for the worst-case scenario," Silva said.

The vessel was carrying 81 containers of "dangerous cargo" including acids and lead ingots.

The escape of microplastic granules from the ship's cargo has already forced a fishing ban and prompted concern for the marine environment as well as the local economy.

Sri Lankan authorities believe the fire was caused by a nitric acid leak which the crew apparently knew about nine days before the blaze started.

Police said three officers from the ship -- two Russians and an Indian -- had been questioned and their passports impounded.

The Singapore-registered ship was heading to Colombo from India. Its 25 crew members were evacuated last week. Two suffered minor injuries.