A wildfires is raging in the foothills above and in the city of Ventura, some 80 kilometres northwest of Los Angeles, threatening more than 12,000 homes.
An unrelenting wildfire fanned by hot, dry Santa Ana winds is threatening more than 12,000 homes in and around Ventura, California, forcing thousands of people to race for safety.
The fire, dubbed the Thomas Fire, raged in the foothills above and in the city of Ventura, some 80 kilometres northwest of Los Angeles, fire officials said late on Tuesday, a day after it began. It had charred more than 50,000 acres (20,235 ha), they said.
"We are still in the middle of an aggressive and active firefight on the ground," said Robert Welsbie, spokesman for the Ventura Fire Department.
"If the winds pick up, we will face quite a challenge."
The fire, which was zero per cent contained, was being whipped by unpredictable Santa Ana winds, which blow in from the California desert.
Wind gusts were forecast to top out at 115 km per hour on Wednesday and remain strong through the week.
There were no immediate reports of fatalities or civilian casualties, Welsbie said.
"The public did an outstanding job heeding our evacuation orders, getting out of these danger zones in a very prompt timely manner," Welsbie said.
Some 1000 firefighters were battling to save homes from the conflagration. One firefighter suffered a minor injury, was treated and released, Welsbie said.
California Governor Jerry Brown declared a state of emergency, freeing state funds and resources to assist.
More than 250,000 homes were without power, utilities said. All schools in the Ventura Unified School District cancelled classes for Wednesday.
The Thomas Fire was the largest of several large blazes that broke out across Southern California following the onset of the Santa Ana winds.
In the San Fernando Valley north of Los Angeles, the so-called Creek Fire had blackened more than 11,000 acres (4450 ha) and forced the evacuation of 2500 homes and a convalescent center north of Interstate 210.
The highway remained open even as other roads were closed, officials said.
Three firefighters were injured and taken to a hospital, where they were in stable condition, the Los Angeles Fire Department said on its website.
Los Angeles Mayor Eric Garcetti declared a state of emergency in the city while 11 Los Angeles Unified schools cancelled Wednesday classes.
Some 30 structures were destroyed by the Creek Fire as of Tuesday evening, the Los Angeles Fire Department said.