Mara Rodriguez, a spokesperson with the San Bernardino County Sheriff's Department, which issues evacuation orders, said nearly 5000 homes fell under the existing orders and nearly 17,000 more were under evacuation warnings.
The blaze threatened thousands of homes and commercial structures as it burned along the edge of the San Bernardino National Forest, about 105km east of Los Angeles.
As of Monday, the blaze had charred about 83 square kilometres of grass and brush and blanketed the area with a thick cloud of dark smoke. It was three per cent contained.
Firefighters were using bulldozers, helicopters and planes to control a rapidly spreading blaze that broke out near a remote-controlled plane airport in Orange County southeast of Los Angeles. The fire spread to about 7.8 square kilometres in only a few hours.
Firefighters battle the Airport Fire in Trabuco Canyon, California. (AP PHOTO)
In northern California, a fire burned at least 30 homes and commercial buildings and destroyed 40 to 50 vehicles in Clearlake City, 117km north of San Francisco, officials said.
Roughly 4000 people were forced to evacuate by the Boyles Fire, which was about 10 per cent contained.
The fires are among the most dangerous of the many burning in various parts of California.
About 32km outside Reno, Nevada, the uncontained Davis Fire grew to about 26 square kilometres after igniting on Sunday afternoon. It originated in the Davis Creek Regional Park in the Washoe Valley and was burning in heavy timber and brush, firefighters said.
An emergency declaration issued for Washoe County noted that about 20,000 people were evacuated from neighbourhoods, businesses, parks and campgrounds.
Parts of south Reno remained under the evacuation notice on Monday, firefighters said, and some homes, businesses and traffic signals in the area were without power.
The Reno fire is roughly 770km to the northeast of the blaze in the San Bernardino National Forest, where firefighters worked in steep terrain in temperatures above 38C, limiting their ability to control the blaze, officials said. State firefighters said three firefighters had been injured.
Wildfires were burning across the west, including in Idaho where fire managers were preparing for an active day, with more challenging conditions expected on Tuesday. The Boulder and the Lava Fires are burning in western Idaho.
In central Oregon, firefighters were dealing with a number of blazes that prompted evacuation warnings, including one west of Mount Bachelor on the Deschutes National Forest that was estimated around 32.4 hectares in size.
18°C