Wind-driven flames ripped through tinder-dry brush and were soon racing towards the Pacific Ocean, incinerating more than 32 square kilometres and putting around 2 000 homes at risk on Thursday.
Television footage showed at least one home ablaze in an isolated canyon as around 600 firefighters fanned out across the vast area to try and staunch the rapidly advancing wall of fire.
"We have conditions that are very dramatic, very dangerous for firefighters. This fire is growing," Ventura County Fire Department spokesperson Tom Kruschke told NBC4 television.
"We are asking members of the public to be very aware – this is very dangerous. This is still a moving fire."
The blaze fanned by strong winds ravaged hillsides and canyons in Ventura County north-west of Los Angeles, threatening homes around the towns of Newbury Park and Camarillo, north of Malibu.
Pacific Coast Highway closed
A 13km section of the scenic Pacific Coast Highway was closed from about 10 miles west of Malibu due the Camarillo Springs fire, the California Highway Patrol said on its Twitter feed.
California State University at Channel Islands announced it was cancelling all classes and activities at its Camarillo site "due to the [fire] and heavy smoke drifting onto the campus".
Live television pictures showed flames and smoke billowing up from the tinder-dry hillside above the Dos Vientos neighbourhood of Newbury Park, where residents were ordered to evacuate.
Helicopters could be seen drawing water from a nearby lake to drop on the flames, in video shown by KTLA 5 television.
Wildfires are common across the western United States in the summer, and in southern California they are often fanned by strong offshore Santa Ana winds that more typically blow up in the fall and winter. – AFP