(CNN) A raging wildfire that forced massive evacuations in Northern California scorched thousands of acres in hours -- and is expected to keep growing.

The Kincade Fire ignited Wednesday night in Sonoma County, and burned 16,000 acres by Thursday night. It was fueled in part by high winds that had already prompted California electric utilities to intentionally cut power to thousands of residents

The blaze had claimed 49 structures by Thursday afternoon, Cal Fire said. It was unclear how many of those lost were homes.

Embers and smoke spread over a hillside near Geyserville.

Embers and smoke spread over a hillside near Geyserville.

Embers fly across a roadway in Jimtown on October 24.

Embers fly across a roadway in Jimtown on October 24.

Trees burn as the fire engulfs a hillside in Geyserville.

Trees burn as the fire engulfs a hillside in Geyserville.

A fire whirl whips across dry brush as the Kincade Fire spreads through Sonoma County on October 24.

A fire whirl whips across dry brush as the Kincade Fire spreads through Sonoma County on October 24.

Cows stand on a ridge as the Kincade Fire approaches in Sonoma County.

Cows stand on a ridge as the Kincade Fire approaches in Sonoma County.

A firefighter monitors the Kincade Fire in Geyserville on October 24.

A firefighter monitors the Kincade Fire in Geyserville on October 24.

Crews build a fire break as the fast-moving blaze burns in the hills above the River Rock Casino near Geyserville.

Crews build a fire break as the fast-moving blaze burns in the hills above the River Rock Casino near Geyserville.

The sun rises above a smoke-filled valley in Geyserville on October 24.

The sun rises above a smoke-filled valley in Geyserville on October 24.

Two firefighters discuss a plan while battling the wildfire in Geyserville.

Two firefighters discuss a plan while battling the wildfire in Geyserville.

Geyserville, about 80 miles north of San Francisco, is among the communities under mandatory evacuation order.

Geyserville, about 80 miles north of San Francisco, is among the communities under mandatory evacuation order.

A structure continues to burn after the Kincade Fire moved through Geyserville, California, on Thursday.

A structure continues to burn after the Kincade Fire moved through Geyserville, California, on Thursday.

Vines surround a burning building as the Kincade Fire burns through the Jimtown community of unincorporated Sonoma County, California, on Thursday, October 24.

Vines surround a burning building as the Kincade Fire burns through the Jimtown community of unincorporated Sonoma County, California, on Thursday, October 24.

Approximately 1,300 personnel are fighting the fire, which was 5% contained.

While the winds had started to die down by Thursday afternoon, officials said, an estimated 2,000 residents were still under evacuation orders.

Among the communities under mandatory evacuation order was the entirety of Geyserville, about 80 miles north of San Francisco. The Sonoma County Sheriff's Office told residents Thursday morning to leave after the fire crossed Highway 128, heading west.

Fire comes during intentional power outages

The fire erupted the same day that California's largest utility started another round of intentional power cuts to prevent its equipment from sparking wildfires. It is burning near the outage footprint in Sonoma County, Pacific Gas & Electric officials said.

Susi Weaver, the manager for a ranch in the Mayacamas Mountains above Geyserville, California, sprays down the dry brush as the Kincade fire burns.

PG&E said in an incident report that a transmission line failed Wednesday about 9:20 p.m. local time.

The utility had a worker out Thursday morning inspecting the line when fire personnel pointed out an apparently broken jumper on a tower. The location on the report is near where the blaze began.

The transmission lines were still active because wind speeds of concern for those are higher than for distribution lines, the company said.

The fire started at 9:27 p.m. Wednesday and the cause is still under investigation, Cal Fire has said.

The latest blackouts will continue at least through Thursday in parts of 17 counties, including Sonoma's wine country. Red flag warnings are in place for more than 25 million people in Northern and Southern California, which means soaring temperatures, low humidity and strong winds will increase fire dangers.

Winds are expected to die down in Northern California by the afternoon, CNN meteorologist Chad Myers said, but could pick back up on Sunday.

JUST WATCHED Hurricane-force wind gusts are rapidly spreading California wildfires Replay More Videos ... MUST WATCH Hurricane-force wind gusts are rapidly spreading California wildfires 01:37

Another big wind event is forecast later Thursday for Southern California, Myers said, where gusts could reach up to 65 mph.

"One spark will take a fire a long way," Myers warned.

Southern California Edison (SCE), another utility in that part of the state, shut off power to more than 15,000 customers in Kern, Los Angeles, Riverside, San Bernardino and Ventura counties.

Farther south, more than 320 customers in Descanso and Alpine lost power after San Diego Gas & Electric turned it off, citing "high winds and dangerous weather conditions."

Two firefighters discuss a plan while battling the Kincade Fire in Geyserville on Thursday.

Blaze burned 5,000 acres in three hours

The Kincade Fire torched more than 5,000 acres within first three hours, Sonoma County Sheriff's Sgt. Juan Valencia said. At that rate, a football field would be burned every three seconds, according to CNN meteorologist Brandon Miller.

The blaze started in the area of the Geysers geothermal plant in Geyserville. The company that operates the plant, Calpine, "de-energized" its local power line system before the fire started, Calpine vice president of external affairs Brett Kerr said in a statement to CNN.

As the fire burned, winds gusted up to 76 mph nearby, the National Weather Service said.

Firefighters confer while battling the Kincade Fire near Geyserville, California, on Thursday.

The sheriff urged residents to heed those evacuation orders, not only for their safety, but for firefighting efforts.

"It helps us to fight the fire," he said, "rather than have to rescue someone from their home."

Ash was "falling like snow," early Thursday in the burn zone, fire data scientist Nicholas McCarthy tweeted, referring to the burned residue as "pyrometeors."

Scanning with @FireWeatherLab at the #KincadeFire. Pyrometeors (ash) falling like snow with Ka radar on hand.



Got my dual purpose sleep/pyrometeor sampling device in overdrive. pic.twitter.com/YpVoLa3viS — Nicholas McCarthy (@mccarthy_nfm) October 24, 2019

In October 2017, the Tubbs Fire ravaged tens of thousands of acres in Sonoma County and killed nearly two dozen people. In Santa Rosa alone, a fire wiped out thousands of homes in the city roughly 50 miles northwest of San Francisco.

Old Water Fire threatens Southern California

Another fire in San Bernardino County in Southern California prompted mandatory evacuation orders for at least 80 homes, according to the San Bernardino National Forest Service.

Firefighters were making progress, the forest service said, and containment was at 30%.