A brush fire burning in southern California has overrun a packed freeway in a mountain pass, torching several vehicles as drivers abandoned their cars and scrambled to safety.

Television images showed firefighting aircraft dropping water onto burning vehicles.

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At least 20 vehicles, including a truck carrying new cars, have been destroyed on the Interstate 15 freeway that links southern California and Las Vegas.

Drivers could be seen standing on the side of the road in the Cajon Pass, their vehicles left stranded in the gridlocked traffic.

The fire, which broke out in the drought-parched foothills of San Bernardino County, had charred more than 3,500 acres as crews battled to get it under control.

There have so far been few reports of injuries.