Residents of San Bernardino awoke early on Thursday to a rapidly-spreading fire covering 200 acres, one of several raging in southern California.
The Hillside fire, east of Los Angeles, spread faster than firefighters could contain it during intense winds.
Another major blaze had erupted on Wednesday dozens of miles away on the far side of Los Angeles.
The US National Weather Service said conditions were “extremely critical and life threatening”.
The strong gusts of wind fanning the flames have at times approached hurricane-level speeds of more than 74mph (119km/h).
In San Bernardino, about 490 homes were evacuated – about 1,300 people, and those evacuations remained in effect by 06:00 local time (13:00 GMT) as more than 500 firefighters tackled the blaze.
The Easy fire, in Simi Valley, was being battled by more than 700 people, Ventura County fire said, and had spread to cover 1,723 acres – an area twice the size of New York’s Central Park.
At one point on Wednesday it threatened to engulf the Ronald Reagan Presidential Library.
Fires across California over the past week have led to mass evacuations and power cuts. Governor Gavin Newsom has declared a state-wide emergency.
As the so-called Santa Ana winds swept in, the National Weather Service issued rare “extreme red flag” warnings for Los Angeles and Ventura counties.
“I don’t know if I’ve ever seen us use this warning,” said forecaster Marc Chenard.
Palls of smoke from the wildfires could be seen from the International Space Station.
Ventura County Fire’s information officer, Mike DesForges, said that more than 1,000 firefighters had been deployed to battle the Easy Fire at one point.
“At the height of the fire, 7,000 homes were evacuated and were directly threatened by fire,” he said.
San Bernardino County Fire chief Kathleen Opliger urged residents to stay away from their homes during the evacuation order.
“We still have a lot of work to do up there to get rid of the hot spots and take care of that,” she said on Thursday.
“This fire moves so fast, and continues to have the potential to move so quickly, that if folks don’t evacuate when we ask them to it’ll be very difficult to try to get them out when the fire is moving towards their home.”
Aircraft carrying water and fire-retardant joined the effort to protect the Ronald Reagan Presidential Library, which is about 40 miles north-west of LA.
Staff were advised to “shelter in place” as emergency crews tackled the flames. Library director Duke Blackwood later announced that the building was out of danger. He said artefacts had already been moved to safety to protect them.
It was later revealed that a herd of goats probably helped to save the hilltop library.
They had been hired to eat an area of flammable shrubs earlier this year, creating a fire break.
Ventura County’s assistant fire chief Chad Cook said the Easy Fire had quickly “outflanked” crews fanned by the winds.
“We did experience gusts up to 65mph this morning which made long-range spotting very, very dangerous and also quickly outpaced the initial attack resources,” he said.
There are fears that the winds will also fan the nearby Getty Fire, which has already scorched 745 acres.
Meanwhile, authorities in northern California said progress had been made in tackling the Kincade Fire which ignited last week.
The fire covered 76,825 acres and triggered evacuation orders for nearly 200,000 people.
On Wednesday, officials said the blaze was 30% contained.
Meanwhile, energy supplier Pacific Gas & Electric (PG&E) cut off power to nearly 400,000 more homes across California on Wednesday as a precaution against damaged power cables starting more fires.
The utility has come in for strong criticism for pre-emptively shutting off power to thousands of properties.
The company says it is a matter of public safety but critics say the precautionary blackouts have been too widespread and too disruptive.
PG&E filed for bankruptcy in January after facing hundreds of lawsuits from victims of wildfires in 2017 and 2018.