Several massive wildfires burned out of control in Napa and Sonoma counties early Monday, destroying an untold number of homes, forcing the evacuation of many thousands of people and shutting down major roadways as firefighters sought to halt the advance of the infernos driven by powerful winds.

There was no immediate information on damage and injuries — nor an explanation for the sheer number of fires — but structures including homes were burning in both counties, according to authorities and witnesses.

Residents described fleeing for their lives in the middle of the night, in cars or on foot. Two hospitals in Santa Rosa, those run by Kaiser Permanente and Sutter Health, were evacuated. People flocked to gas stations in cities that were safe from the conflagrations, to fuel up and buy water and other supplies.

The series of fires began to ignite Sunday and multiplied as the night went on, impacting five counties. In Mendocino County, authorities evacuated communities near Redwood Valley and Willits. In Marin County, officials said at 3 a.m. that a grass fire had closed part of Highway 37. In Alameda County, fire crews from multiple jurisdictions were battling a blaze in the North Berkeley Hills at 3:45 a.m.

All over the region, flames raced across fields and freeways and skies filled with embers and ash. The National Weather Service said the blazes, which caused power outages and blanketed much of the Bay Area in smoke, were fanned by strong and dry northeast winds.

In Napa County, the Atlas Fire broke out near Atlas Peak Road and blackened hundreds of acres in a famed wine-growing area northeast of the city of Napa and the Silverado Trail. A second Napa County blaze to the northwest, near Calistoga, forced residents to flee their homes as well.

Guests of the Silverado Resort and Spa on Atlas Peak Road said they had been evacuated in a rush as flames approached. The resort had hosted the Safeway Open, a PGA Tour event, which ended Sunday.

“We were sleeping, but we kept smelling smoke,” said Chris Thomas, 42, of Kirkland, Wash., who arrived in the Napa Valley late Sunday with his wife, Marissa Schneider, for a wine-tasting trip.

They saw a firetruck pass, then were ordered to leave by loudspeaker. The power went out. Then things went downhill fast.

“It was surreal,” Thomas said. “When I started loading stuff into the car it was a hell-storm of smoke and ash. There were 30 to 40 mph winds. I couldn’t even breathe, so I ran back to the unit to get Marissa. It was so smoky I went to the wrong unit. When I found her I said, ‘Forget it, let’s just go.’ It went from being an annoying evacuation to something really scary.”

Schneider said, “Debris was gusting around. The flames were about 100 feet from our door. It was scary.”

They drove to downtown Napa and found a hotel room, though they were wary of being evacuated again.

Evacuation centers were set up at the Napa County Fairgrounds at 1435 North Oak St. in Calistoga and CrossWalk Community Church at 2590 First St. in Napa.

In the Kenwood area, east of Santa Rosa, evacuations were ordered along Porter Creek, Petrified Forest, Franz Valley and Mountain Home Ranch roads.

In northern Santa Rosa, evacuations were ordered for residents and businesses in the Skyfarm Drive, Fountaingrove Parkway and Montecito Heights areas east of Highway 101, according to the Police Department.

Just after 2 a.m., though, Santa Rosa police reported the fire had jumped Highway 101 and “ignited structures” west of the freeway near a Kohl’s department store on Hopper Avenue. Evacuations were then ordered for that area.

“This is a life threatening event,” officials said. “Leave immediately.”

Among those who left the Hopper Avenue area were 11 members of the Flores family, who woke up and piled into two vehicles with four dogs after being jolted awake by neighbors. They said the air was thick with smoke and the wind was blowing so hard that trash bins toppled over.

“We couldn’t really see anything,” said Bradley Flores, 15. “We just got our dogs and got into the car and left. The wind was so bad our car was shaking.”

He spoke from the parking lot of a Chevron gas station in Petaluma. The lot was full of evacuees who were fueling up, buying water and talking on cell phones.

Santa Rosa evacuees were directed to the Finley Community Center in that city, and when it filled up, were steered to Santa Rosa’s Veteran’s Memorial Building at 1351 Maple Ave. or the Petaluma Community Center at 320 North McDowell Ave.

Also in Petaluma were Lance and Barb Cottrell, who live near Santa Rosa. At about midnight, they had seen fire cresting over the ridge near their home, after neighbor rang the doorbell. They packed a couple of suitcases, grabbed some prized antiques and headed to a friend’s house to the west of Highway 101.

“Our house is probably gone,” Lance said. “We just finished it in 2014.”

Soon, though, flames raced so fast into their friend’s neighborhood that neighbors ran for their lives. Lance jumped in his car, and Barb in hers, and they tried to drive away, but they they saw a house engulfed in front of them and had to flip a U-turn. They ended up stuck in traffic before escaping down country roads west of Santa Rosa, avoiding trees that had blown down.

The scene was similar in Napa County. On Highway 121 between Sonoma and Napa, flames chewed up vegetation on both sides of the road, shooting embers as a stream of people fled the area. Some drivers pulled over to the side of the road at safe spots, looking back at the fires. Police and firefighters tried to keep people moving.

Sonoma County officials said emergency dispatchers were being “overwhelmed by 911 calls” from residents smelling smoke, adding, “Please only call 911 if you see actual unattended flames.” Authorities in Marin and San Francisco counties made the same plea, asking residents who smell smoke not to call 911 unless they see flames.