■Nine Los Angeles firefighters injured in fuel tank explosion.

■Two firefighters critically injured, seven others also hurt

■Explosion occurred while battling a truck fire

LOS ANGELES — A burning truck’s fuel tank exploded early Thursday while Los Angeles firefighters were trying to battle the blaze, injuring nine of them, including two critically, fire officials said.

All nine were rushed to Harbor-UCLA Medical Center and were stabilized, said Dr. Molly Dean, a trauma surgeon. One of the critical patients had to be intubated and was transferred to a burn unit at Los Angeles General Medical Center.

Of the other injured, four suffered moderate injuries and three had minor injuries, said Capt. Erik Scott. a fire spokesperson.

Mass Casualty Incident

“Essentially, we had a mass casualty incident, tragically, of our own members,” Scott said.

In a TV news helicopter video, discarded firefighting gear could be seen at the site where the injured crew members were initially treated.

The explosion occurred six minutes after firefighters arrived on the scene.

Details of the Explosion

The vehicle was the tractor portion of a big rig and was fueled by compressed natural gas carried in two 100-gallon (378-liter) tanks, one of which exploded, Scott said.

“That explosion was significant,” he said. “The ball of flame was as high as these telephone poles, and it actually did explode one of the transformers nearby.”

The truck was completely destroyed, and firefighters stayed well back as a small flame continued to burn in the mangled wreckage, the helicopter footage showed. Scott said the second fuel tank was “still off-gassing and therefore there’s a minor threat.”

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Aftermath of the Explosion

The driver had stepped away from the truck to call 911 and was not injured. After the explosion, some 160 firefighters responded.

The blast occurred adjacent to an industrial area separated from a neighborhood by a wide street and a rail line.

Wilmington is 18 miles south of downtown, near the ports of Los Angeles and Long Beach.