VIDEO: 'I might die here': Videos show drivers escaping wildfire on I-5 in Shasta County near Redding
Flames are on both sides of Interstate 5, forcing the closure of a nearly 50-mile stretch.
It has destroyed thousands of trees - some 70 feet (20 meters) tall - that could fall onto the roadway, said Denise Yergenson, a spokeswoman for the state Department of Transportation.
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"There is lots of damage, lots of emergency personnel. It's just not a safe situation," she said.
Officials planned to reevaluate whether to reopen the highway that traverses the entire West Coast from Mexico to Canada and serves as a main artery for commerce.
Caltrans said it needs to replace guard rails, signs and fix the pavement.
VIDEO: Woman grateful to be alive after fleeing Shasta Co. wildfire
Several million dollars in business is being lost each day due to the closure because trucks cannot get through, according to Caltrans.
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(The Associated Press contributed to this report.)