A large brush fire erupted in Simi Valley early Wednesday and was quickly burning toward neighborhoods, triggering mandatory evacuations amid strong Santa Ana winds.

The Easy fire, which is burning along Tierra Rejada Road, started near the 118 Freeway and Madera Street shortly after 6 a.m. About 250 acres burned in the first hour, said Ventura County Fire Capt. Brian McGrath.

The evacuation area was described as a box: Tierra Rejada Road to the north, Olsen/Madera Street to the south, Madera Street to the east and Highway 23 to the west. A shelter has been set up at the Thousand Oaks Community Center at 2525 N. Moorpark Rd.

It is not clear how the fire started. The blaze is burning near the Ronald Reagan Presidential Library.

Video footage from the scene showed wind-whipped flames rapidly consuming a large swath of hillside in the area. All Simi Valley public schools were closed because of the fire.

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The fire comes amid dangerous weather conditions and the threat of more blackouts as utilities attempt to reduce wildfire risk.

Santa Ana winds of 50 to 70 mph, with isolated gusts of 80 mph, will be the strongest to hit the region in recent memory and sparked urgent preparations for more potential fires and evacuations. The winds are expected to continue through Thursday.

“The magnitude of the wind gusts really are going to be a concern,” said Daniel Swain, climate scientist with UCLA and the National Center for Atmospheric Research. “The actual winds that people experience really will be quite extreme in a lot of places, really everywhere except for the wind-sheltered parts of downtown L.A. and central L.A.”

Pacific Gas & Electric Co. said it could shut off power to well over 1 million people in its latest bid to reduce wildfire risk.

The blackout would cover more than two dozen Northern California counties and would come just days after a much larger power shut-off that left more than 2 million people in the dark over the weekend.

To the south, the forecast of extreme Santa Ana winds prompted Southern California Edison to say it could shut off power to more than 350,000 households in Los Angeles, Ventura, Santa Barbara, San Bernardino and Riverside counties.

Fire danger from power lines was underscored Tuesday when L.A. officials said a Los Angeles Department of Water and Power line hit by a tree branch sparked the Getty fire.