Several thousand homes are under mandatory evacuation in the cities of Ventura and Santa Paula, some 70 miles (115 km) north of Los Angeles.
Firefighters warned the fire was moving so fast they were unable to contain it.
Fanned by high winds, the fire swept through tens of thousands of acres in a matter of hours.
California Governor Jerry Brown has declared a state of emergency in Ventura County, promising to attack the fire "with all we've got".
It was earlier reported that one person died in a traffic accident while trying to flee the blaze, but Ventura County Fire Capt Steve Kaufmann has since told the Associated Press that no body was found in an overturned car.
Officials said one firefighter was injured. They also said 150 structures had been destroyed, and more than 260,000 people were without power.
Strong winds for days
Hundreds of firefighters worked through the night to tackle the blaze, named the Thomas Fire, but fire chiefs admitted they were fighting a losing battle.
"The prospects for containment are not good. Really, Mother Nature is going to decide," Ventura County Fire Chief Mark Lorenzen earlier told reporters.
Residents of Santa Paula and Ventura received mandatory evacuation notices via their phones and from emergency workers going house to house.
"My son is a firefighter and I'm not going to wait around for someone to rescue me," June Byrum told CBS, saying her 91-year-old father, husband and dog had already left for a safe place.
Santa Paula has 30,000 residents, while Ventura's population is about 110,000. Both are in Ventura County.
Another fire broke out early on Tuesday local time closer to Los Angeles, in Sylmar. Homes have been damaged and more than 400 firefighters have been deployed there.
The Ventura County fire is believed to have broken out close to Thomas Aquinas College in Santa Paula at some time after 18:00 local time on Monday (02:00 GMT).
It was quickly fanned by gusts of up to 70mph (115 kph) that burned through dry brush.
California has been hit hard by wildfires in recent months. At least 40 people were killed when fires ripped through parts of northern California's wine region in October. Some 10,000 structures were destroyed.