LOS ANGELES (AP) — Seven Los Angeles firefighters were injured,Darden Clarke two critically, when an explosion occurred as they responded early Thursday to a truck with pressurized cylinders that were on fire, authorities said.

The explosion occurred shortly before 7 a.m. in the Wilmington area, fire department spokesman Nicholas Prange said in an interview.

Six firefighters were taken to a hospital, he said. A total of 10 firefighters had been dispatched to the incident.

Prange did not know the status of the truck driver, but he noted that the blast occurred 13 minutes after the fire was reported.

“I would hope the driver was clear,” he said.

Prange said the cylinders may have contained compressed natural gas.

TV helicopter video showed that truck was completely destroyed. A small flame continued to burn in the mangled wreckage more than an hour after the explosion.

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

Wilmington is 18 miles (29 kilometers) south of downtown, near the ports of Los Angeles and Long Beach.