A fast-moving wildfire that has forced hundreds of people to flee from their homes in the drought-parched foothills northwest of Los Angeles had blackened some 20,000 acres by Saturday evening and was threatening homes, say fire officials.
The so-called Sand Fire broke out shortly after 2pm on Friday and spread quickly near Santa Clarita, about 65 kilometres northwest of Los Angeles, forcing the evacuation of some 300 people.
As darkness fell across Southern California on Saturday the blaze was only 10 percent contained, throwing a pall of thick black smoke over much of Los Angeles.
Residents posted pictures on social media of the sun blotted out by the towering plumes and the South Coast Air Quality Management District issued a smoke advisory, warning of unhealthy air conditions in the region.
Fire over Los Angeles pic.twitter.com/1IGFmRCdVs— ZephyrDogTown (@zephyrdogtown) July 23, 2016
One firefighter sustained a minor injury but as of Saturday morning no structures had been destroyed, officials said. No deaths have been reported.
"Because this is the fifth year of an ongoing drought we have a lot dry vegetation," Los Angeles County Fire Chief Daryl Osby told a news conference.
"Some of these fuels, they haven't burned in decades. This fire has increased to about 11,000 acres just overnight."
Some 900 firefighters were battling the flames in temperatures exceeding 41°C, with the aid of 28 helicopters and eight fixed-winged aircraft.
But fire managers said crews were struggling in very rugged terrain as they tried to defend homes in the community of Little Tujunga and stop the spreading blaze that is burning through chaparral and brush.
Evacuation shelters have been set up for residents in the area and about 10 roads have been closed due to the fire. A number of roads in and out of foothill communities were shut down.
The fire is one of a series this summer that have hit the drought-stricken state, where dried grass and bush land as well as high temperatures have helped fuel the blazes.