Firefighters and police cleared residents from neighbourhoods near Camarillo before homes were set ablaze by embers blown 3km from the fire front, Ventura County fire department Captain Tony McHale said.
"It's like trying to put out a blowtorch with a squirt gun," said McHale of the fire, which started in a hillside canyon on Wednesday then tore west, driven by Santa Ana winds.
Fuelled by abundant grass and scrub, with wind gusts up to 130km/h, the blaze had burned more than 8000 hectares by Thursday evening, authorities said.
Several civilians were injured and a "significant" number of homes, businesses and other structures destroyed, McHale said.
More than 30,000 people live in the potential path of the fire, California authorities say. (AP PHOTO)
The Los Angeles Times said it had counted more than 90 destroyed homes.
More than 30,000 people live in the potential path of the fire, according to the California Department of Forestry and Fire Protection.
A red flag warning for high winds was in effect until Friday.
Climate scientists say warming temperatures have created wet winters that allowed California's coastal chaparral - small trees, shrubs and bushes - to thrive.
Record temperatures this summer dried out hillsides, priming them for wildfire.
The United States is experiencing a strong wildfire year, with 3.2 million hectares burned to date, compared with an annual, full-year average of 2.8 million during the past decade, according to National Interagency Fire Center data.
California wildfires have in 2024 burned more than three times as much land as last year at this time when the state's fire season was more benign, according to government data.
