The largest and most destructive of the wildfires plaguing southern California has destroyed more than 430 homes and buildings northeast of Los Angeles, officials said.
The wind-whipped blaze has burned nearly 180 square miles (466 square kilometres) in Ventura County, stretching from hilly forests to the Pacific Ocean.
It is only 5% contained and gusty Santa Ana winds that have driven the fire are expected to continue.
Officials said on Thursday night they had made good progress battling much of the fire, but that thousands of homes remained in jeopardy.
Dozens of trailer homes in a retirement community were destroyed by the blaze, which also killed race horses at an elite training facility.
The fire tore through the tightly packed Rancho Monserate Country Club community in the small city of Fallbrook, known for its avocado orchards and horse ranches.
At least two people were hospitalised with burns.
As the flames approached the elite San Luis Rey Downs training facility for thoroughbreds, many of the more than 450 horses were cut loose to prevent them from being trapped in their stalls if barns caught fire, said Mac McBride of the Del Mar Thoroughbred Club.
Horse trainer Scott Hansen said he knows that some of his 30 horses at the facility died.
"I don't know how many are living and how many are dead," he said. "I guess I'll have to figure that out in the morning."
Most of the horses were saved, Mr McBride said, and were being loaded to go to the Del Mar Fairgrounds.
Some ranchers posted urgent pleas on Twitter for help moving horses, including Rawhide Ranch, well-known for running horse riding camps for children and teens.
Thursday's fire prompted the closure of state Highway 76 in both directions and evacuations in an area near the Camp Pendleton Marine Corps Base. Evacuation centres were set up in schools and casinos.
The fire and a smaller one 12 miles (19 kilometres) north in the city of Murrieta broke out the day after state officials sent an unprecedented alert to cell phones across seven southern California counties warning that strong Santa Ana winds could cause extreme fire danger.
Although hurricane-force winds predicted did not materialise, firefighters faced gusts that fanned flames and put thousands of homes in jeopardy.
Along the coast between Ventura and Santa Barbara, tiny beach communities were under siege as fire raged from steep hillsides across US Highway 101.
"We drove through a wall of flames," Wendy Frank said, describing her ordeal after evacuating her horses from Ojai on Wednesday night. "I didn't know if we'd make it. I just put the accelerator down. I know we were going over 100 mph, we could have been going much more, and just hoped for the best."
Fires flared up on Thursday along the highway, forcing an evacuation of the dozens of homes at Faria Beach.
"Anyone in your homes still, you need to leave now," a California Highway Patrol officer said through a loudspeaker while driving down a smoke-shrouded street. "The fire is here, you need to leave."
The highway, which runs the length of the state and is a major commuter corridor to Los Angeles, was closed intermittently along the 28-mile (45-kilometre) stretch between Ventura and Santa Barbara.