Two rapidly growing wildfires burning a few kilometres apart in parched foothills just northeast of Los Angeles are threatening to merge and are forcing the evacuation of more than 700 people.
The blazes come as California and other southwestern US states bake in a heat wave at the official start of summer that is imposing gruelling conditions on firefighters and stoking flames in dry brush.
The so-called Fish Fire and the Reservoir Fire, both raging in Angeles National Forest, more than doubled in size on Monday night and were entirely unconfined, the US Forest Service said in a statement.
The Fish Fire had grown to 1214 hectares by early morning while the Reservoir Fire stood at about 971 hectares, according to the US Forest Service.
"It is a possibility that the two fires would merge," Andrew Mitchell, a spokesman for the team battling the Reservoir Fire, said.
The fires burning more than 32 km northeast of downtown Los Angeles have forced at least 700 people to evacuate, Mitchell said.
The cause of the fires, fuelled by dry brush, chaparral and worsened by extreme heat, are under investigation.
Meanwhile, a half-dozen other wildfires burned uncontrollably across California, from as far south as the California-Mexico border to the far northern California city of Yreka, according to the California Department of Forestry and Fire Protection.
Firefighters have made steady progress in controlling the so-called Sherpa Fire, a seven-day old blaze northwest of Santa Barbara, California, that has burned nearly 3237 hectares in an area of ranches and campgrounds.
That fire is 70 percent contained, according to tracking website InciWeb.
Two states away, the Dog Head Fire in central New Mexico has charred more than 6880 hectares and was 46 percent contained after destroying 24 homes and 21 minor structures soon after it broke out last week.