About 1,000 US firefighters are tackling wildfires near Los Angeles, which have caused two deaths, with 12,000 people driven from their homes.
The first major wildfires of the season threaten hundreds of houses north of the city, in the San Fernando Valley.
Southern California is vulnerable to wildfires between October and February when the warm, dry Santa Ana winds blow in, drying out vegetation.
Governor Arnold Schwarzenegger declared a state of emergency in two counties.
The order covers Los Angeles and Ventura.
"Winds are causing fire conditions to change by the hour, which is why it is so important that residents in the areas surrounding these wildfires heed warnings from public safety officials to evacuate," Mr Schwarzenegger said.

'Very dangerous'
In the San Fernando Valley, one fire in the Porter Ranch area has consumed more than 5,000 acres (2,000 hectares) while another in Lake View Terrace has burnt 5,300 acres, according to the LA Times newspaper.
A homeless man living in a wood and cardboard shelter beneath a motorway junction was found dead.
A second person died when a car crashed on a stretch of motorway near one of the fires, which was reportedly shrouded in smoke.
"It's a very dangerous situation," said Los Angeles County Fire Chief P Michael Freeman as he urged residents to leave danger areas.
"You may not even be able to outrun the fire if you're that close to it."