Canyons, hillsides and residential areas in densely populated areas have been affected, and the fires have destroyed hundreds of homes and forced many schools in Los Angeles to close.
Authorities fear that four major fires - ranging from LA up the Pacific coast to Santa Barbara County - may be whipped up by the region's notorious westward Santa Ana winds, which could reach hurricane strength.
The winds, which blow in hot and dry from the California desert, could reach 75mph and create "extreme fire danger", according to an alert from the countywide emergency system in Los Angeles.
The National Weather Service said high winds were not expected to die down until at least the end of Saturday.
The fires, which broke out on Monday and Tuesday, have reached the wealthy enclave of Bel Air in LA.
No civilian casualties or deaths have been reported but three firefighters were injured, the Los Angeles Fire Department said.
The Los Angeles Unified School District, the country's second largest with more than 640,000 students, said it closed at least 265 of almost 1,100 schools.
Dozens of schools have also been closed in neighbouring Ventura County, where the Thomas fire, the largest of the blazes, has charred more than 96,000 acres.
The fires have created apocalyptic scenes of flaming mountains and walls of smoke, with firefighters spraying water and helicopters dumping bucketloads in attempts to contain the flames.
Jake Sandell, a resident in Santa Paula in Ventura County, said: "You don't expect things like this.
"I was expecting this year to see snow on that mountain and now the thing is on fire."
Because of the heavy smoke, the South Coast Air Quality Management District has warned residents, especially the elderly, children, pregnant women and people with respiratory diseases, to stay indoors.
In the San Fernando Valley north of LA, the Creek fire has destroyed at least 30 homes, blackened more than 12,000 acres and forced the evacuation of 2,500 homes and a health centre.
Another blaze, the Rye fire, threatened more than 5,000 homes and structures northwest of Los Angeles.(c) Sky News 2017: Southern California wildfires force 200,000 people to flee their homes