Fire crews on Thursday were battling a wildfire that sprang up in Southern California stoked by strong winds, destroying multiple homes and forcing over 10,000 people to flee.

The fast-moving Mountain Fire, which started in Ventura County northwest of Los Angeles on Wednesday morning, has burned nearly 20,000 acres and was 0% contained as of late morning Thursday, according to the state wildfire-fighting agency Cal Fire.

The evacuation area was expanded Thursday morning and now includes 12 zones. Ventura County Fire Capt. Trevor Johnson said suppression efforts are focused on the northeast section of the blaze, close to the city of Santa Paula. With 19,643 scorched acres, the fire has grown by more than 5,000 acres since the morning.

At least two people have been hospitalized for smoke inhalation, officials said. An estimate of the number of damaged or destroyed structures will not be available until an assessment has been completed, the fire department said.

Evacuation orders will remain in place through Thursday, the county said, adding that at least 800 firefighters from across the state were battling the blaze and more are expected.

Tanker planes were only used in a limited capacity Wednesday to drop water and fire retardant because of the gusty winds, but Fire Capt. Tony McHale said they may be more widely employed Thursday if the winds die down somewhat as expected. Johnson said instead of planes, helicopters doused the fire with water all night.

The National Weather Service warned Thursday that critical wildfire weather across the state, fueled by gusty winds and low moisture, would linger for the next few days. Santa Ana winds are expected to hit 30-55 mph and gusts up to 100 mph are possible in mountainous areas through Friday.

The Federal Emergency Management Agency on Wednesday authorized the use of federal funds to help California battle the fire.

Fire threatens thousands of homes, other buildings

Cal Fire has not yet released an official count of how many homes and other structures were destroyed, but reporters and photographers with the Ventura County Star, part of the USA TODAY Network, witnessed homes burning throughout the day near Camarillo and Somis.

The fire was threatening over 3,500 structures, Gov. Gavin Newsom said Wednesday. Photos show firefighters working in huge plumes of smoke and houses completely engulfed, some leveled by the fire.

"Bushes are burning, grass is burning, hedgerows are burning, agricultural fields are burning, and structures are burning," Fire Chief Dustin Gardner said. "This fire is moving dangerously fast."

Milder weather coming, but still a tough road ahead

Thursday's forecast calls for offshore winds of 25-35 mph through the afternoon, leading to a red-flag warning remaining in place until 6 p.m. Conditions should improve with a milder, more typical onshore wind early in the evening.

However, Johnson pointed out firefighters are grappling with treacherous terrain on the northeast part of the blaze, which has become their focus.

“The fire there is in a tricky place,'' Johnson said at a news conference. "It’s rugged, steep ground that only our finest firefighters can even access to work in there. So we have aircraft working there to pin it down. They’re coming up with multiple options.’’

Drew Smith, assistant chief of the Los Angeles County Fire Department, said the strong winds can carry embers for up to three miles, making it much harder to contain the blaze.

“These fires when we’re on our high-risk days of Santa Ana winds are different from when we have our fires during the summer that are not in a wind-dominated fire environment,’’ Smith said.

Extreme fire weather across California on Thursday

About 26 million people across California remained under red flag warnings Thursday.

That includes areas along the Interstate 5 corridor and the northern Ventura County mountains through Friday. "Particularly dangerous situation" (PDS) red flag warnings were extended through later Thursday morning in the San Fernando Valley, Santa Clarita Valley, central and southeastern Ventura County Valleys and Ventura County inland, stretching to beaches from Malibu to Oxnard.

"These are extremely critical and highly volatile conditions," the weather service in Los Angeles/Oxnard said. "Any new fires in the Red Flag Warning area – and especially the PDS Red Flag Warning area – will have rapid fire spread, extreme fire behavior, and long-range spotting."

Ventura County officials said power might be proactively shut off to prevent any new fires from sparking during these conditions, and over 90,000 customers were impacted as of Thursday morning.

Contributing: Thao Nguyen, USA TODAY; The Ventura County Star.