A massive explosion at 3a.m. EDT on one of the two barges still ablaze in the Mobile River in Mobile, Ala., on Thursday, April 25, 2013.

A Carnival cruise ship was evacuated after an explosion on several nearby fuel hours.

MOBILE, Ala.—Firefighters on Thursday extinguished a huge blaze that erupted hours earlier when two fuel barges exploded, leaving three people with critical burns and forcing the evacuation of crew from a nearby cruise ship.

The cause of the explosions remained under investigation, but investigators believe it was likely from a spark caused by a crew cleaning the barges, Coast Guard Lt. Mike Clausen said.

Firefighters from Mobile and Coast Guard officials responded to the pair of Wednesday night explosions involving the gas barges in the Mobile River east of downtown. More explosions followed over the next few hours.

Authorities say three people were brought to the University of South Alabama Medical Center for burn-related injuries. The three remained in critical condition Thursday morning, hospital spokesman Bob Lowry said.

Across the river, workers were evacuated from the Carnival Triumph, the cruise ship that became disabled in the Gulf of Mexico in February before it was towed to Mobile’s port for repairs. A cruise spokesman said none of its workers were injured and there was no damage to the ship.

Alan Waugh, who lives at the Fort Conde Inn across.