An “extreme red flag warning” was in effect Wednesday morning for much of Los Angeles County as firefighters worked to increase containment lines around the Getty Fire burn area in the Sepulveda Pass.

“Adverse weather conditions will be the biggest challenge for firefighters,” Los Angeles Fire Department spokeswoman Margaret Stewart said.

“In anticipation of the extreme Santa Ana wind event, the LAFD has recalled and staffed additional resources for any emergency that may arise over the next 24 hours. These resources will be strategically placed in key locations that have a history of being prone to wildfire.”

The National Weather Service issued the warning, which went into effect at 11 p.m. Tuesday, amid predictions some mountain areas could be blasted with gusts of up to 80 mph. The warning covers the bulk of Los Angeles County and will remain in effect until 6 p.m. Thursday.

“This Santa Ana wind event will likely be the strongest we have seen so far this season,” according to the weather service.

The fire has burned at least 656 acres and was 15% contained as of 7 p.m. Tuesday, with 12 homes destroyed and five others damaged. One firefighter sustained a minor injury.

“It does take one ember, just one ember downwind, to start another brush fire,” LAFD Chief Ralph Terrazas warned during a Tuesday afternoon briefing attended by Gov. Gavin Newsom, Mayor Eric Garcetti and a host of other officials.

The danger posed by the high winds was made painfully clear again Wednesday morning when a fast-moving brush fire broke out in Simi Valley along Tierra Rejada Road, south of the 118 Freeway and near the Ronald Reagan Presidential Library.

The Los Angeles County Fire Department is sending Firehawk water dropping helicopters to Simi Valley as part of its mutual aid agreement. L.A.’s city fire department is not yet sending any resources because Ventura County has not yet made any mutual aid requests from the department, fire department spokesman Brian Humphrey said.

The fire was threatening homes, and officials said evacuations were being ordered in the suburban Ventura County community. Schools were closed for the day.

The Los Angeles County Sheriff’s Department said it was monitoring the newest blaze.

The Getty Fire was reported shortly after 1:30 a.m. Monday by a witness who called the California Highway Patrol and reported seeing flames on a hillside close to the 405 Freeway near Getty Center Drive, along with a possible power line on fire, according to the CHP.

The fire raced to the west and southwest, burning its way in the direction of Pacific Palisades and marching through some of the Southland’s priciest real estate.

At the fire’s height, evacuation orders were issued affecting 10,000 structures, both residential and commercial, in an area between the San Diego Freeway and Temescal Canyon Road, from Sunset Boulevard north to Mulholland Drive. Evacuation orders were lifted Monday night for the Mountaingate community south of Mulholland.

As of Tuesday afternoon, the LAFD reported that 7,091 residences were still in the evacuation zone.

Garcetti said despite Tuesday’s relative calm in the fire area, evacuees should plan to be away from their houses for at least another day, likely longer, due to the dangerous winds. He said authorities don’t want to lift evacuations prematurely, only to order people back out when winds accelerate.

Evacuation centers remain open at the Westwood Recreation Center at 1350 S. Sepulveda Blvd., near Wilshire Boulevard, and the Palisades Recreation Center, 851 Alma Real Drive.

Evacuation centers for animals were established at the West Valley Animal Shelter at 20655 Plummer St., the West Los Angeles Animal Shelter at 11361 Pico Blvd. Hansen Dam Recreation Center at 11770 Foothill Blvd. in Lake View Terrace was opened to receive large animals.

All schools in Malibu and some in the Los Angeles Unified School District were closed Wednesday, while all schools in Santa Monica were scheduled to be open.

Because of the anticipated winds and fire risks, red flag parking restrictions mandated by the Los Angeles Fire Department went into effect at 8 p.m. Tuesday to keep narrow, hilly streets clear to allow fire trucks unimpeded passage. The restrictions would remain in effect until 8 p.m. Thursday, but could be extended depending on conditions, the LAFD said.

“We’re doing everything we can to wrap our arms around this fire to be able to prevent a potential of those strong gusty Santa Ana winds pushing the fire, rekindling a lot of the fire and blowing embers a mile to two miles down range,” LAFD Assistant Chief Jamie Moore said Tuesday morning.

Authorities confirmed Tuesday afternoon the Getty Fire was caused by gusting winds that severed a tree branch and blew it into a Department of Water and Power electrical line, causing sparks that fell onto the brush below.

“This was, simply put, … an act of God,” Garcetti said.

Terrazas added, “There is no evidence of arson. It is an accidental start.”

Marty Adams, general manager of the Department of Water & Power, told reporters the agency had just completed a brush-clearing operation in the area in July, trimming 248 trees “in excess of what the state requires.” He noted that the branch in question came from a tree “outside of our clearance zone” but was carried by the wind into the power line.

Adams said the power line itself remained intact and is still delivering electricity to the area.

Nearly 1,200 firefighters were assigned to the Getty Fire, with crews using bulldozers to create fire breaks and extend containment lines.

The San Diego Freeway, a southbound stretch of which was closed for much of the day Monday, was open through the Sepulveda Pass, but exit ramps between the Ventura (101) Freeway in Sherman Oaks to Sunset Boulevard were blocked.

The Getty Center museum was not believed to be in immediate danger from the flames. Officials there said Getty Center and the Getty Villa in Pacific Palisades would be closed through Friday to ensure fire crews had adequate access to the area to fight the flames.