MONTEBELLO, Calif. >> An overpass that was scorched by a fiery gasoline tanker crash on a major Southern California freeway will be partially demolished, forcing thousands of commuters onto detours indefinitely, authorities said Thursday.

Engineers who examined the blackened Paramount Boulevard overpass on State Highway 60 determined that the eastern lanes must be torn down immediately, California Highway Patrol Officer Luis Mendoza said.

"There’s too much structural damage," he said. "They don’t think it can support weight on top."

Crews were waiting for heavy equipment to arrive to begin the work, he said. The western lanes of the overpass, in the Los Angeles suburb of Montebello, were still being inspected but most of the fire was concentrated on the eastbound lanes, he said.

Demolition will take the entire weekend and reconstruction could stretch on for many days more, Mendoza said.

A 10-mile stretch of the road was shut down after the double-tanker carrying some 9,000 gallons of gasoline caught fire under the overpass. The intense heat partially melted the truck, cratered the roadway and left spilled fuel everywhere.

A Montebello firefighter suffered a broken leg fighting the blaze and thousands of motorists were stuck in place for hours. The truck’s driver and a passenger escaped unharmed.

The cause of the crash, including the possibility that the tanker’s brakes overheated, remained under investigation.

State Highway 60 is a major artery linking downtown Los Angeles with the San Gabriel Valley and other bedroom communities east of the city. It also is a main route for trucks delivering goods from the Ports of Los Angeles and Long Beach to inland warehouses.

On Thursday morning, the usually bumper-to-bumper morning commute in the Los Angeles area was even more of a misery as tens of thousands of drivers who normally used State Route 60 took detours.

Delays of an hour or more were reported, Mendoza said.

"It’s definitely impacting just about every freeway that comes into Los Angeles County. It’s causing overflow onto the 210, the 10 and the 91," CHP Officer Mike Harris said.

Nakisa Kohanchi, an Iranian immigrant, missed her naturalization ceremony because of the traffic jams.

Kohanchi left her home in the Sherman Oaks area of Los Angeles at 7:15 a.m. and headed to the ceremony in Montebello, 20 miles away.

It took her nearly two hours to get there, as she was routed off State Highway 60, got lost and drove in circles.

"I had to exit the freeway and I didn’t know how I could get there from the streets," said Kohanchi, who planned to become a U.S. citizen at a second ceremony scheduled later in the day.

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Associated Press Writer Robert Jablon in Los Angeles contributed to this story.