LOS ANGELES – A compressed natural gas tank exploded on a big rig in Wilmington Thursday morning, injuring at least seven firefighters, including two who were hospitalized in critical condition, authorities said.

The blast occurred shortly before 7 a.m. at Alameda Street and North Henry Ford Avenue.

Firefighters had responded to the scene after getting reports that cylinders believed to be compressed natural gas (CNG) were on fire.

“There are two 100-gallon tanks on that vehicle, one of which exploded while our firefighters were putting out the fire,” Captain Erik Scott of the L.A. Fire Department said at a mid-morning news conference.

The natural gas, Scott said, was the truck’s fuel, and the cab was not hauling a trailer at the time.

“That explosion was significant. The ball of flame was as high as telephone poles, and it did explode one of the [power] transformers nearby,” said Scott.

Sky5 aerial footage showed the charred wreckage of the big rig with burned debris scattered around the area, including firefighting gear.

Scott said the injured firefighters were quickly triaged and treated at the scene before getting transported to a local hospital.

“Two of them are in critical condition as we speak,” Scott said.

The second CNG tank remained intact at 9 a.m., forcing fire crews to keep a safe distance.

The driver appeared to escape unharmed prior to the blast.

“Our heart and concern remain with our dear firefighters who suffered those significant traumatic injuries,’ Scott said.

Motorists were asked to avoid the area.

Check back for updates on this developing story.