By JOCELYN GECKER and NOAH BERGER

GEYSERVILLE, Calif. (AP) — A Northern California wildfire exploded in size early Thursday amid dangerous winds that prompted the state’s largest utility to impose electrical blackouts to prevent fires.

Authorities ordered the entire community of Geyserville to evacuate after the fire in the Sonoma County wine region north of San Francisco grew to more than 15 square miles (39 square kilometers). The town has about 900 residents and is a popular stop for wine country tourists.

The cause of the blaze was not yet known, but wildfire risk was extremely high as humidity levels plunged and winds gusted up to 70 mph (113 kph). There were no immediate reports of any injuries.

The fire came two years after a series of deadly blazes tore through the same area, killing a total of 44 people.

Mary Ceglarski-Sherwin and her husband, Matt Ceglarski-Sherwin, lost their Santa Rosa rental home during one of those fires and fled the flames again early Thursday when Mary’s asthma awakened her around 2:30 a.m. Their power was still on when they grabbed their small dogs, some clothes and emergency kits they acquired during the last fire.

“I told him, ‘We gotta go, we gotta go; I can feel it changing,‘” Mary Ceglarski-Sherwin told the Santa Rosa Press-Democrat. “By the time we got out there, we could feel the heat and see the smoke.’”

At least two fires have erupted in Southern California, but they have remained small.

Utilities in California have said the rolling blackouts are designed to keep winds that could gust to 60 mph (97 kph) or more from knocking branches into power lines or toppling them, sparking wildfires. Electrical equipment was blamed for setting several blazes in recent years that killed scores of people and burned thousands of homes.

The Pacific Gas & Electric Co. began rolling blackouts Wednesday stretching from the Sierra foothills in the northeast to portions of the San Francisco Bay Area, impacting a half-million people — or nearly 180,000 customers. PG&E warned that a second round of outages could occur over the weekend when winds were forecast to return.

Southern California Edison said Thursday that it had cut power to more than 15,000 customers as hot and dry Santa Ana swept parts of Southern California. The utility was considering additional power cuts to more than 286,000 customers.

The San Diego Gas & Electric utility said it cut power to about 328 customers.

The latest outages come two weeks after PG&E shut down the power for several days to about 2 million people in northern and central California.

“We understand the hardship caused by these shutoffs,” PG&E CEO Bill Johnson said. “But we also understand the heartbreak and devastation caused by catastrophic wildfires.”

The small city of Calistoga, in the Napa Valley, known for its hot springs and wineries, was among those hit by Wednesday’s outages.

“Right now, we have no wind. Zero. I don’t even see a single leaf blowing. Did they really have to cut the power right now?” he said, shortly after the lights went out and he revved up the generators. “When the wind picks up to 40 mph maybe that’s a good time to close the power.”

“They’re not appreciating enough the impact this has on everybody,” he said about PG&E.

Sonoma County Supervisor James Gore said PG&E was better this time about getting information to people who would be affected, but he was still astonished by the need to resort to largescale blackouts.

“I am a big believer in shutdowns to prevent fires. But the thing that erodes public trust is when it doesn’t make sense,” he said. “You say, ‘God, I know if we can put a man on the moon … we can manage a (power) grid.’

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Gecker reported from San Francisco. Associated Press writers Janie Har in San Francisco and John Antczak and Christopher Weber in Los Angeles contributed to this report.