COLOMBO, Sri Lanka (AP) — An explosion occurred Tuesday on a ship anchored near Sri Lanka's capital on which a fire had been burning for several days, prompting the crew's evacuation, officials said.

The container vessel MV X-Press Pearl was anchored about 9.5 nautical miles (18 kilometers) northwest 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 Capt. Indika de Silva said crew members and salvage and firefighting experts evacuated the ship 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, Silva said.

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