A Singapore-flagged container ship on its way to Navi Mumbai caught fire off the coast of Kerala on Monday, the Indian Coast Guard said.

While four of the ship’s 22 crew members were missing, the remaining had been rescued, it added. A search operation was underway to rescue the missing persons.

The 18 members of the crew had reportedly jumped into the sea and used emergency rafts to escape the fire that broke out in the middle portion of the ship MV Wan Hai 503, The Hindu quoted officials of the Kerala State Disaster Management Authority as saying.

The rescued crew was taken to Mangaluru in Karnataka for treatment, OnManorama reported.

The incident took place when the vessel was off the coast of Beypore port, the news outlet reported. The Indian Coast Guard said that the ship was 130 nautical miles north-west of Kochi.

There were reportedly more than 650 containers, including 150 containing hazardous materials, in the cargo vessel, The Hindu reported. Twenty containers had fallen into the sea after several explosions and fire on board.

A container explosion had triggered the fire, OnManorama reported. The ship remained adrift and continued to emit smoke as of Monday night.

Five coast guard ships and an aircraft were dispatched to rescue the crew and for surveillance, The Hindu quoted officials from the Maritime Rescue Sub Centre in Kochi as saying.

The vessel had departed Colombo, Sri Lanka on Saturday and was expected to reach Mumbai on Tuesday.

Singaporean High Commissioner Simon Wong said on social media: “Professional and rapid response of the Indian Coast Guard and the Indian Navy. Praying that remaining crew are found soon.”

While two of the four missing persons are Taiwanese citizens, one is from Indonesia and another from Myanmar.

The ship’s owners have been requested to assess and report the nature of the cargo in the affected hold to ascertain the presence of hazardous material. No information has been yet received on whether dangerous goods were involved in the explosion, The Indian Express reported.

This came two weeks after a Liberian-flagged container vessel carrying “hazardous cargo” sank off the coast of Kochi on May 25 after it began gradually tilting a day earlier. All 24 crew members on board the vessel were rescued.

On May 29, the Kerala government declared the wreckage of the container ship a state-specific disaster. It was carrying 13 containers with hazardous cargo and 12 of calcium carbide.