By 10 p.m., the fire had spread to 15,000 to 20,000 acres, fire officials said. There was no estimate of containment.
The U.S. Forest Service said at least five structures were ablaze, though it was unclear what type of structures they were.
Three firefighters sustained minor injuries.
Authorities ordered the immediate evacuations of areas from San Francisquito Canyon Road north to Elizabeth Lake Road, Lake Hughes and areas south of Lake Hughes Road and north of South Portal Road, Lake Hughes.
Lake Hughes was under mandatory evacuation and Lake Elizabeth was under voluntary evacuation. At least 1,000 structures were threatened and 2,000 residents were evacuated.
Evacuation orders remain in effect for as many as 300 homes in Green Valley. Some roads remain closed as the firefight continued. Only residents and emergency personnel are allowed to enter San Francisquito Canyon Road from Copper Hill, and only emergency personnel can enter the areas between Calle Daggett and the Department of Water and Power Village on the San Francisquito Canyon Road. Elizabeth Lake Canyon Road is closed from Cottonwood to Castaic. Cottonwood camp grounds continue to be closed.
Around noon Saturday, Los Angeles County sheriff's deputies evacuated the 41600 Block of Lake Hughes Road, north of Mendenhall Probation Camp due to the blaze. Friday afternoon, Camp Mendenhall and areas north of South Portal Road and west of San Francisquito Canyon were evacuated due to the fire.
A Red Cross evacuation center was established at Marie Kerr Park at 2723 Rancho Vista Blvd. in Palmdale.
Hot and dry conditions are the main challenges for firefighters. Some power lines near the fire zone are also posing a concern. According to fire officials, if the fire moves in the predicted north, northwest direction, it could burn directly under those power lines.
More than 900 firefighters and 10 aircraft were working to tame the fire.
The blaze broke out Thursday afternoon north of Santa Clarita, along San Francisquito Canyon Road. Firefighters called the blaze ferocious and relentless.
Two firefighters have been injured - one was struck by a rock on Thursday and another was treated for heat exhaustion Friday afternoon.
Crews are dealing with extremely rugged terrain, making the firefight very difficult.
The cause of the fire remains under investigation.
Local health officials warned that air quality in the Santa Clarita Valley and San Gabriel Valley mountains will be unhealthy for sensitive individuals throughout the weekend due to the fire, and they urged residents to take precautions and stay indoors if possible.