A travel alert has been issued as at least 27,000 residents were forced to flee their homes in the middle of the night as fast-moving wildfires ripped through southern California.
Several thousand homes are under mandatory evacuation in the cities of Ventura and Santa Paula, some 70 miles north of Los Angeles.
Three large wildfires in Ventura and Los Angeles County are actively destroying homes and other structures.
The Foreign and Commonwealth Office warned in an updated travel advisory: “Thousands are under mandatory evacuation orders. Several smaller fires have developed in the region and the fire risk remains extremely high.
“The fires are being exacerbated by dry conditions and sustained winds around 35-45 miles per hour, with gusts reaching 80 miles per hour.
“Under these conditions wildfires can spread swiftly, so you should remain cautious.
“Monitor local media reports and follow the advice of local law enforcement officials, including any evacuation orders.”
The alert came as California governor Jerry Brown declared a state of emergency in Ventura County.
More than 1,000 firefighters are now battling the fires, which have burned 45,500 acres.
Officials said one firefighter was injured, 150 structures had been destroyed, and more than 260,000 people were without power.
“The prospects for containment are not good. Really, Mother Nature is going to decide,” Ventura County fire chief Mark Lorenzen earlier told reporters.