An explosion on a ship anchored near Sri Lanka’s capital Colombo has prompted the crew’s evacuation.

The container vessel MV X-Press Pearl was anchored about 9.5 nautical miles (18km) 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 tonnes 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 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.

Sri Lankan authorities said experts from the Netherlands and Belgium were surveying the ship, while India had promised to send vessels and an aircraft to help fight the fire.

Aerial photos released by Sri Lanka’s air force showed the vessel engulfed in flames and thick smoke. Strong 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.