Flames fanned by strong winds in the Angeles National Forest burned close to high-voltage electrical lines Thursday afternoon, and mandatory evacuations were being ordered as a brush fire raged out of control.
About 400 acres had been burned as hundreds of firefighters battled the blaze, officials said.
The Powerhouse fire in San Francisquito Canyon north of Castaic had burned at least one structure as thick clouds of smoke billowed into the air, according to television news footage.
Mandatory evacuations were being ordered in the Green Valley area, the Los Angeles County Sheriff's Department said.
The blaze, stoked by 24 mph gusts, was burning close to high-voltage lines, some of which power Los Angeles. But no outages had been reported, according to Southern California Edison and the Los Angeles Department of Water and Power.
San Francisiquito Canyon Road was closed at Copper Hill Drive to Elizabeth Lake, the California Highway Patrol said.
The blaze had charred at least 300 acres after breaking out shortly before 4 p.m. in an area not far from Castaic Lake, the CHP said.
Helicopters and fixed-wing aircraft were aiding more than 300 firefighters on the ground, said Nathan Judy, an Angeles National Forest spokesman.
He said commanders on the grounds were ordering more helicopters and air tankers.