Ferocious Santa Ana winds raking southern California have whipped up explosive wildfires, prompting evacuation orders for thousands of homes.
The biggest blaze broke out in Ventura County and grew wildly to more than 48 square miles in the hours that followed, sheriff's sergeant Eric Buschow said.
Another fire erupted on the north edge of Los Angeles, threatening the Sylmar and Lakeview Terrace neighbourhoods, where residents scrambled to get out.
At least 150 structures had burned so far in Ventura County, officials said.
TV reports showed homes in flames as well as Vista del Mar Hospital, a facility that treats patients with mental problems, chemical dependency and veterans with post-traumatic stress syndrome.
More than 27,000 people have been evacuated and one firefighter was injured in Ventura County. There was no word on the extent of the injuries.
After initial reports of a fatality, county fire captain Steve Kaufmann said a dead dog was found in an overturned car but no people .
The winds were pushing the fire towards Santa Paula, a city of some 30,000 people about 60 miles north-west of Los Angeles. Many of the evacuated homes were in that city.
However, evacuation orders were expanded to houses in Ventura, which is 12 miles south west and has 106,000 residents.
"The prospects for containment are not good," Ventura County fire chief Mark Lorenzen said before dawn. "Really, Mother Nature is going to decide."
Thomas Aquinas College, a school with about 350 students, has also been evacuated, with students going to their own homes or to those of faculty and staff, the college said in a statement.
The fires were being driven by southern California's notorious gusty and dry Santa Ana winds, which have been linked to some of the region's worst wildfires.
Typical of autumn, the Santa Anas are spawned by high pressure over the Great Basin that sends air flowing towards southern California, where it speeds up as it squeezes down through mountain passes and canyons and blows out towards the coast.
Wind speeds at some locations in Ventura County were well over 60mph.
Forecasters said winds would continue through until Thursday.