An explosion on a ship anchored near Sri Lanka’s capital, on which a fire had been burning for several days, has prompted the crew’s evacuation, officials said.

The container vessel MV X-Press Pearl was anchored about nine and a half nautical miles north-west of Colombo and waiting to enter its port when the fire erupted four days ago, the Sri Lankan navy said.

It said it believes the fire was caused by chemicals being transported on the Singapore-flagged ship. The ship was carrying 1,486 containers, including 25 tons of nitric acid and other chemicals, which it loaded at the port of Hazira, India, on May 15, it said.

The vessel’s 25-member crew includes Philippine, Chinese, Indian and Russian nationals.

Navy spokesman Captain Indika de Silva said the ship was evacuated of crew members and salvage and firefighting experts after the explosion.

Several containers also tumbled into the sea, he said.

Aerial photos released by Sri Lanka’s air force showed the vessel engulfed in flames and thick smoke. High winds intensified the blaze, Capt Silva said.

Five tugboats were engaged in firefighting efforts and a navy ship was anchored nearby to help them, he said.

X-Press Feeders, which owns and operates the ship, confirmed the crew was safe and said it would work closely with Sri Lankan authorities and emergency services to extinguish the blaze and save the vessel and its cargo.

“Specialised firefighting equipment which arrived from Europe last night will join the salvaging operations,” according to a statement on its website.