A major wind-driven wildfire in California wine country exploded in size overnight, forcing hundreds to evacuate.

Wind gusts early Thursday topped 70 mph.

“Authorities ordered all 900 residents of the 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,” reports CBS News.

The direct cause of the fire — called the Kincade Fire — was unknown, but the Associated Press notes that “strong, dry winds … have affected much of the state,” including Sonoma County.

Although the winds eased after daybreak, the Kincade Fire continued to spread across hilly terrain that rises to 3,000 feet above sea level. Later in the morning, a second fire was reported in Sonoma County.

“It’s a lot of grass and oak woodlands and then you go into trees,” Cal Fire deputy chief Scott McLean told SFGate.com. “There’s a lot of rolling ground and then there’s steep topography that’s difficult to access. Then you deal with the population and structures in middle of it.”

Firefighters, McLean said, “definitely have a fight on their hands.”

So far, no injuries have been reported, nor are there any estimates of the number of buildings damaged or destroyed by the Kinkaide Fire. A series of wildfires struck the same area two years ago, killing 44 people.

One of two wildfires in Southern California, called the Old Water Fire, burned between 50 and 100 acres with zero containment early Thursday, CBS reports.

A spokesperson for the San Bernardino National Forest told CBS Los Angeles that the fire had “extreme potential” for large growth as Santa Ana winds began to pick up. Some evacuations were ordered.  See video from San Bernardino above.

Power companies moved to shut off electricity to the affected areas because of the threat that high winds could knock trees onto power lines, sparking more fires.

Pacific Gas & Electric “began rolling power outages Wednesday stretching from the Sierra foothills in the northeast to portions of the San Francisco Bay Area, affecting a half-million people,” SFGate says.

Southern California Edison shut down electricity to more than 15,000 customers and was considering additional cutoffs. San Diego Gas & Electric cut power to several hundred customers.

PG&E warned that a second round of outages could take place over the weekend near San Francisco, when forecasters say winds are likely to return.

“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.”