Multiple explosions aboard two fuel barges near Mobile, Ala., led to a major fire Wednesday night that left three people critically injured with burns and created a situation so unstable that fire and rescue officials decided to let the fire burn into the night.

Firefighters from Mobile and U.S. Coast Guard officials responded after 8:30 p.m. CDT to a pair of explosions involving the gas barges in an area of the Mobile River east of downtown, authorities said.

As they were responding, a third explosion occurred at about 9:30 p.m., Mobile Fire and Rescue spokesman Steve Huffman wrote in an email to The Associated Press. Three more explosions followed over the next few hours.

The Coast Guard said early Thursday that a one-nautical-mile safety zone had been established around one barge, which it identified as an "empty compressed natural gas barge that was at the dock for cleaning."

Authorities said three people were transported to University of South Alabama Medical Center after suffering burn-related injuries. Huffman identified them as workers with Oil Recovery Co.

The three were in critical condition early Thursday, according to nursing administrator Danny Whatley.

Fire officials said they planned to let the barges burn overnight.

The Carnival Triumph, the cruise ship that became disabled in the Gulf of Mexico last February before it was towed to Mobile's port, was evacuated, said Alan Waugh, who lives at the Fort Conde Inn in downtown Mobile, across the river from the scene of the explosions. Waugh saw the blasts and said throngs of Carnival employees and others were clustered on streets leading toward the river as authorities evacuated the shipyard.

"It literally sounded like bombs going off around. The sky just lit up in orange and red," he said, "We could smell something in the air, we didn't know if it was gas or smoke." Waugh said he could feel the heat from the explosion and when he came back inside, his partner noticed he had what appeared to be black soot on his face.

U.S. Coast Guard Petty Ofc. Carlos Vega said the initial blast took place in a ship channel near the George C. Wallace Tunnel _ which carries traffic from Interstate 10 under the Mobile River. The river runs south past Mobile and into Mobile Bay, which in turn flows into the Gulf of Mexico.

Video from WALA-TV (http://bit.ly/15NEYJl) shows flames engulfing a large section of the barge, and a video that a bystander sent to AL.com (http://bit.ly/13vWz4G) showed the fiery explosions and billowing smoke over the river.

The cause of the explosion was not immediately clear, Huffman and Vega said. Huffman wrote early Thursday that the incident involved "two barges, six explosions so far."

"It is raw gas, gas without additives," he wrote.

Mobile Fire Chief Steve Dean told AL.com he was confident the fire _ which he said involves gas like what would be found at a service station pump _ wouldn't spread to nearby industrial properties, including the shipyard where the Carnival cruise ship is docked.

The explosion comes two months after the 900-foot-long Triumph was towed to Mobile after becoming disabled on the Gulf during a cruise by an engine room fire, leaving thousands of passengers to endure cold food, unsanitary conditions and power outages for several days. The ship is still undergoing repairs there, with many workers living on board.

Carnival didn't immediately respond to an emailed request for comment late Wednesday.

Earlier this month, the cruise ship was dislodged from its mooring by a windstorm that also caused, in a separate incident, two shipyard workers to fall into Mobile Bay. While one worker was rescued, the other's body was pulled from the water more than a week later.

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Associated Press writer Phillip Lucas in Atlanta contributed to this report.