Firefighters in California are battling a new fast-moving blaze threatening thousands of homes and the Ronald Reagan Presidential Library and museum.

It comes as rare "extreme" red flag warnings are in place for much of the Los Angeles region.

The so-called Easy Fire in the Simi Valley northwest of Los Angeles erupted around 6am local time, forcing the evacuation of the Reagan library and nearby homes as it spread to more than 1,300 acres, officials said.

Fire crews backed by tanker helicopters raced to protect the hilltop library surrounded by dense brush from the flames raging out of control and fed by powerful wind gusts.

Some 200 horses and other animals at area ranches were also being evacuated, with people rushing from outside the region to help.

"The fire outflanked us very rapidly, pushed by those 40 to 50 mile-per-hour winds," Ventura County Fire Assistant Chief Chad Cook told reporters.

"We did experience gusts up to 65 miles an hour this morning, which made long-range spotting very, very dangerous and also quickly outpaced the initial attack resources."

Ronald Reagan's Air Force One sits on display at the Reagan Presidential Library as the Easy Fire burns in the hills in Simi Valley, California

Ventura County Sheriff Bill Ayub said 7,000 homes were under evacuation orders affecting some 26,000 residents.

He said the blaze had also led to the evacuation of inmates held at a jail in the region.

Melissa Giller, a spokeswoman for the library, told local radio that the archives and much of the memorabilia from the Reagan administration were safely stored in an underground fireproof vault at the facility.

The flames were closest to a pavilion housing a former Air Force One aircraft.

Authorities said it was unclear what caused the fire, which started near Easy Street.

The fire broke out amid "critical" or "extremely critical" red flags warnings in parts of southern California because of powerful so-called Santa Ana winds, with potential gusts of up to 130km/ph in mountainous areas.

"We expect the Santa Anas to be howling," the National Weather Service said.

Some 18 million Californians live in areas affected by the red flag warnings.

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Closer to Los Angeles, firefighters were battling the Getty Fire, which began near the famous Getty Center museum on Monday and by today had burned 745 acres, with 27% containment.

Authorities said they feared the fire, which was caused by a tree branch that fell on power lines, could spread because of the strong winds expected to last through tomorrow evening.

"It does take one ember, just one ember downwind, to start another brush fire," Los Angeles Fire Department (LAFD) Chief Ralph Terrazas has warned.

LAFD spokeswoman Margaret Steward said that in anticipation of the record-strong Santa Ana winds, all staff had been mobilised and additional backup brought in.

"These resources will be strategically placed in key locations that have a history of being prone to wildfire," she said.

Mandatory evacuations were also ordered today in the Jurupa Valley, about an hour's drive east of Los Angeles, after a fire broke out near a freeway and quickly spread to 100 acres.

Farther north, in Sonoma County, Cal Fire, the California fire department, said firefighters had made progress overnight battling the Kincade Fire, which has consumed 76,825 acres and led to mandatory evacuation orders affecting nearly 200,000 people.

More than 5,000 firefighters backed by 600 fire engines, 27 helicopters and air tankers were battling the inferno, which has destroyed 206 homes and commercial properties, including several wineries, and was now 30% contained, Cal Fire said.

California Governor Gavin Newsom has declared a statewide emergency because of the fires and the state's largest utility, Pacific Gas and Electric, has been imposing rolling blackouts in the northern and central parts of the state in a bid to reduce the fire risk.

Other utilities in the southern part of the state have also shut off power to customers.

The wildfires spreading through the state come as California is still reeling from the aftermath of the most destructive wildfire in state history - the Camp Fire, which destroyed the town of Paradise and killed 86 people last year.

Similar blazes in northern California, including in the Napa and Sonoma wine regions, killed 44 people in 2017 and destroyed thousands of structures.