The Powerhouse Fire grew to 19,500 acres in northern Los Angeles County after a hot and windy Saturday, burning structures and prompting evacuations in rugged areas between the Santa Clarita and Antelope valleys.
At least five homes have burned in the blaze, said Los Angeles County Fire spokesman Keith Mora.
About 1,000 structures were threatened in the burn area, he said.
Three firefighters have been injured, and 960 firefighters, assisted by planes and helicopters, were expected to keep up the aerial and ground assault against flames on Saturday. The blaze was 20 percent contained, said John Wagner of the U.S. Forest Service.
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The USFS told NBC News the fire had burned 19,500 acres as of 2:15 a.m. PT Sunday. That was up from 5,561 acres as of 1:40 a.m PT.
Temperatures reached the triple digits in some areas, including near the fire.
Also on Saturday, officials ordered evacuations for Elizabeth Lake Road and areas south of Lake Hughes, and upheld existing evacuations in the San Francisquito Canyon area.
Road closures were also ordered as far south as Castaic at Lake Hughes Road.
The fire broke out Thursday near a hydroelectric plant known as Powerhouse No. 1 in San Francisquito Canyon, north of Santa Clarita.
Health officials urged people to avoid unnecessary outdoor activities as air quality in the Santa Clarita Valley and San Gabriel Mountains was expected to be unhealthy throughout the weekend due to the fire.
Evacuation orders were expected to remain in effect at least through Saturday night for the following areas: the Forest Service's Cottonwood Campground, L.A. County's Camp Mendenhall juvenile detention center and areas along Lake Hughes Road, Judy said. Other evacuations remained for areas north of South Portal Road and west of San Francisquito Canyon Road.
Power lines were reported threatened at one point Thursday, but there were no reports of service disruptions, Judy said.
The cause of the fire was under investigation.
A Red Cross evacuation center was set up at the Marie Kerr Park's recreation center at 2723-A Rancho Vista Boulevard in Palmdale. An evacuation center for large animals has been set up at the Antelope Valley Fairgrounds at 2551 West Avenue H in Lancaster.