LOS ANGELES — The wind-driven wildfire outside Los Angeles that led to the evacuation of the Ronald Reagan Presidential Library has forced about 30,000 residents from their homes and injured three firefighters, authorities said Wednesday night.

More than 1,000 firefighters were battling the Easy fire in Simi Valley, in Ventura County about 50 miles northwest of downtown Los Angeles. No cause had been determined, authorities said, but Southern California Edison Co., or SCE, told state regulators that it was investigating unexplained "circuit activity" about the time the fire was reported at 6:09 a.m.

The blaze had burned through 1,648 acres and was at 0 percent containment, Ventura County fire officials said Wednesday night. About 30,000 residents remained under mandatory evacuation orders, mainly in Moorpark and Thousand Oaks, they said.

Division Chief John Spykerman, the incident commander, told reporters that three firefighters were being treated at hospitals. He said that their conditions weren't available but that they had likely suffered smoke inhalation.

County Fire Chief Mark Lorenzen told reporters on Wednesday afternoon that the fire broke out as fierce Santa Ana winds swirled around the region, with sustained winds of 40 mph "and fuels that were ripe and ready to carry a fire."

"Unfortunately, it was about the worst time it could happen," Lorenzen said.

It hasn't rained in Simi Valley for 125 days, and much of Southern California was under an extreme red flag fire warning as winds occasionally gusted to 70 mph.

SCE, the largest electric utility in the southern part of the state, pre-emptively cut off power on Wednesday to around 82,300 homes and businesses, roughly equivalent to about 205,750 people, as of 10 p.m. according to its website.

Like Pacific Gas and Electric Corp., or PG&E, in Northern California, SCE has been shutting off electricity in rolling blackouts to prevent downed or faulty power lines from sparking new wildfires during the autumn fire season.

"We were prepared for this," Assistant Fire Chief Chad Cook, the incident commander, said at a news conference. But "the fire outflanked us very rapidly today, pushed by those 40- [to] 50-mile-per-hour winds."

"It quickly outpaced the initial attack resources," he said.

Duke Blackwood, executive director of the Reagan library and museum, said he and others were at the site and sheltering in place with flames on multiple sides of the complex.

As Blackwood spoke to NBC Los Angeles, flames could be seen flaring up on a patch of brush just a few feet behind him. But the director insisted the library was safe.

"We were able to protect the Reagan Library. ... Fire moved around the perimeter of the Reagan Library, and we had a successful stand up there," Cook said.

Flames got to within 50 feet of the library grounds, but firefighters were able to beat them back, museum officials said.

"The fire is surrounding us, on our main Presidential Drive and behind our Air Force One Pavilion," where the 40th president's plane is stored, said Melissa Giller, chief marketing officer for the Ronald Reagan Presidential Foundation.

But she told NBC News that because of a fire break, a barrier of cleared vegetation around the building, and water drops from helicopters and planes on Wednesday, "everyone feels completely safe and that the structures will be saved."

Download the NBC News app for breaking news and politics

The Reagan library is in the middle of a zone that was designated for mandatory evacuations in southeastern Ventura County on Wednesday.

Even though the library seemed to be out of immediate harm by early afternoon, the nearby grounds were still susceptible to fire, and officials said high winds could blow dangerous embers from miles away.

"The entire footprint under the fire is still under threat," Cook added.

Simi Valley is a popular area among horse owners, and authorities told equestrians to evacuate their animals to the Ventura County Fairgrounds or the Rancho Potrero Equestrian Center in Thousand Oaks.

Classes were canceled at nearby Moorpark College and at all public schools in Moorpark and Simi Valley on Wednesday. The area's highways, State Routes 23 and 118, were largely closed.

Fierce seasonal winds — known as Santa Ana winds in the southern part of the state and as Diablo winds in the north — have been especially strong this week, sparking dozens of wildfires the length of the state.

In addition to the Easy fire, firefighters were battling the Getty fire near the J. Paul Getty Museum in one of Los Angeles' ritziest areas. The fire, which forced former Gov. Arnold Schwarzenegger and Los Angeles Lakers superstar LeBron James to flee, had burned 745 acres and was 39 percent contained Wednesday evening, the Los Angeles Fire Department said. Twelve residences have been destroyed and another five have been damaged.

Crews made progress on Wednesday against the biggest and most dangerous fire, the Kincade fire north of San Francisco, where at one point tens of thousands of residents had been under mandatory evacuation orders.

Containment of the 76,825-acre fire doubled overnight was up to 45 percent, authorities said, and evacuation orders in several counties were lifted or downgraded to advisories. Conditions were still dangerous, however, and about 365,000 customers remained without power Wednesday afternoon in PG&E's fourth major safety blackout of the month.

Sonoma County Sheriff Mark Essick said Wednesday night that deputies had arrested 10 people in the previous 24 hours on suspicion of prowling or entering evacuation zones without authorization, which he said meant looting.

"Wow, what a week," he said. "Seems like we've been doing this for a month. It's been a week."

Alex Johnson reported from Los Angeles. David K. Li reported from New York.

CORRECTION (Oct. 30, 2019, 6 p.m.): A previous version of this article misstated Chad Cook's title. He is an assistant chief of the Ventura County Fire Department, not the chief.