The Hughes fire, about 80km north of Los Angeles, sent huge flames and plumes of smoke over a hilly area and further taxed firefighters who have managed to bring two major fires in the metropolitan area largely under control.
In just a few hours on Wednesday, the new fire grew to two-thirds the size of the Eaton Fire, one of the two monster conflagrations that have ravaged the Los Angeles area.
The affected area was not as populated as those blazes, said a spokesperson for the firefighters, Matthew Van Hagen.
Ten of thousands of residents have been told to evacuate as a fire spreads north of Los Angeles. (AP PHOTO)
"It's more sparsely populated. However, out here, we are dealing with high winds, which we also saw with the other fires, along with ... a very receptive fuel bed and steep topography again," he said as firefighters battled the fire into the night.
Officials warned people in the Castaic Lake area of Los Angeles County that they faced "immediate threat to life," while much of southern California remained under a red-flag warning for extreme fire risk due to strong, dry winds.
Some 31,000 people were under mandatory evacuation orders and another 23,000 face evacuation warnings, Los Angeles County Sheriff Robert Luna told a press conference.
Los Angeles residents have been warned that smoke from the wildfire could carry toxins. (AP PHOTO)
The Angeles National Forest said its entire 2800 square km park in the San Gabriel Mountains was closed to visitors.
As a result of the red-flag warning, some 1100 firefighters were deployed around Southern California in anticipation of fast-moving fires, the California Department of Forestry and Fire Protection (Cal Fire) said.
More than 4000 firefighters were working on the Hughes Fire, Los Angeles County Fire Chief Anthony Marrone said.
Southern California has gone without significant rain for nine months, contributing to hazardous conditions, but some rain was forecast from Saturday through Monday, possibly giving firefighters much-needed relief.
Helicopters scooped water out of a lake to drop on the fire while fixed-wing aircraft dropped fire retardant on the hills, video on KTLA television showed. Flames spread to the water's edge.
While the new fire raged, the two deadly fires that have ravaged Los Angeles since January 7 came under greater control, Cal Fire said.
The Eaton Fire that scorched 57 square km east of Los Angeles was 91 per cent contained, while the larger Palisades Fire, which has consumed 95 square km on the west side of Los Angeles, stood at 68 per cent contained.
Since the two fires broke out on January 7, they have burned an area nearly the size of Washington, D.C., killed 28 people and damaged or destroyed nearly 16,000 structures, Cal Fire said. At one point, 180,000 people were under evacuation orders, according to Los Angeles County officials.
Private forecaster AccuWeather projects damage and economic losses at more than $US250 billion ($A399 billion).
Reuters
