The Hughes Fire in the Castaic Lake area of Los Angeles County forced evacuations with warnings of "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 19,000 people, a number roughly equal to the entire population of the community of Castaic, were under mandatory evacuation orders, according to Los Angeles County officials. Another 16,000 were under evacuation warnings.
Los Angeles County, the state of California and the US Forest Service said their firefighters were responding. The Angeles National Forest said its entire 280,000ha park in the San Gabriel Mountains was closed to visitors.
As a result of the red-flag warning, some 1000 firefighters were deployed around Southern California in anticipation of fast-moving fires, the California Department of Forestry and Fire Protection (Cal Fire) said.
Helicopters scooped water out of a lake to drop on the fire, video on KTLA television showed, as flames spread to the water's edge.
Interstate 5, a major north-south highway, was closed in the area of the fires due to poor visibility, the California Highway Patrol said.
While the new fire raged, the two deadly fires that have ravaged Los Angeles came under greater control, Cal Fire said.
The Eaton Fire that scorched 5600ha east of Los Angeles was 91 per cent contained, while the larger Palisades Fire, which has consumed 9500ha on the west side of Los Angeles, stood at 68 per cent contained.
Containment measures the percentage of a fire's perimeter that firefighters have under control.
Since the two fires broke out on January 7, they have burned an area nearly the size of Washington DC, 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 $US250 billion ($A400 billion).
A series of smaller wildfires has been extinguished or brought largely under control in Southern California the past two weeks.
