The fire that broke out in the engine room of the New Diamond on Thursday morning had spread to the bridge of the ship, carrying about 2 million barrels of oil, though it has not reached the cargo area, the Sri Lankan navy said.
Director-General of Operations Rear-Admiral Y N Jayarathna told reporters it was the navy's view that there was no real danger of a spill, because the fire on the ship has been contained in the rear section of the vessel.
"The live flames have now died down and there is only white smoke emanating from the vessel," he told a televised press conference.
A navy spokesman, Captain Indika de Silva, said there were 23 crew on board, one of whom is presumed dead. The rest have been taken off the ship by the Sri Lankan navy, with one injured crew member flown to the capital Colombo for treatment.
Three tug boats, five Sri Lankan navy ships as well as two craft from the Russian navy and three from the Indian navy have been assisting in an operation to fight the fire and tow the ship away from the coast, after it began drifting towards land.
At present the vessel is being held by the salvage team in deep sea 35 kms (21.7 miles) east of the Sri Lankan town of Pottuvil, de Silva said.
Initially, the ship was stranded 38 kms (24 miles) east of the town of Thirukovil, but drifted within 25 kms of the coast after being abandoned. Authorities were now towing it eastward, away from the coast, de Silva said.
Thirukovil is a town in Sri Lanka's Ampara district that was badly battered by the 2004 Indian Ocean tsunami. Arugam Bay, a world-renowned surfing spot, is nearby.
"The missing Filipino sailor is presumed dead. He was badly injured when a boiler exploded," de Silva told Reuters, citing crew who were rescued.
"There were five Greek and 18 Philippine nationals among the crew. One of them was injured and he was airlifted out of the ship and the rest were accounted for."
Sri Lanka's meteorology department had already modelled the impact of 70,000 tonnes of crude oil - a quarter of the ship's cargo - spilling into the ocean.
The simulation, a worst case scenario according to authorities, found that such a spill would not immediately threaten the country's east coast.
But Dharshani Lahandapura, chair of Sri Lanka's federal Marine Environment Protection Authority, told Reuters that any spill from the ship would be catastrophic for marine life.
"It will be a huge environmental and economic disaster if this happens," she said.
The 1989 oil spill from the Exxon Valdez, considered one of the worst human-caused environmental disasters, spewed about 37,000 tonnes of crude into waters off Alaska.
The 20-year old New Diamond, chartered by Indian Oil Corp (IOC), had sailed from the port of Mina Al Ahmadi in Kuwait, loaded with Kuwait Export Crude, Refinitiv Eikon tracking data showed. It was heading for the Indian port of Paradip, where state-run IOC has a 300,000 barrel-per-day refinery.
(Reporting by Waruna Karunatilake and Arjuna Ranawana in Colombo; Writing by Sanjeev Miglani and Alasdair Pal; Editing by Clarence Fernandez, Raju Gopalakrishnan and Emelia Sithole-Matarise)
By Arjuna Ranawana and Waruna Karunatilake