(Recasts with recovery effort, adds details on damage, injuries)
By Jim Christie
NAPA, Calif., Aug 24 (Reuters) - Authorities in California's wine country north of San Francisco were scrambling late Sunday to reach damaged buildings and restore power in the town of Napa after a 6.0 magnitude earthquake struck before dawn, injuring more than 100 people.
The temblor damaged historic buildings, set some homes on fire and caused power and water outages around picturesque Napa, a famous wine-producing region and tourist destination.
The quake, the biggest in the region in 25 years, jolted many residents out of bed when it hit at 3:20 a.m. (1020 GMT). It was centered 6 miles (10 km) south of the city of Napa.
There were no known fatalities, but three people were seriously injured, including a child who suffered multiple fractures after a fireplace fell on him, local fire battalion chief John Callahan said. Six fires broke out, including one that consumed six mobile homes, he said.
At least 33 buildings in the city of Napa, a city of 77,000, had been "red-tagged," meaning they were unsafe to enter, said Napa Community Development Director Rick Tooker. Inspectors had accessed about a third of all structures and planned to complete the work on Monday.
Napa's Queen of the Valley Medical Center said it had treated 172 patients injured in the quake.
"They say it went for 50 seconds. It felt like 50 minutes. I was just too terrified to even scream," said Patricia Trimble, 50, the owner of an antique store. She rushed to her store in central Napa and found the front window blown out, cabinets on their sides and merchandise littering the floor.
California Governor Jerry Brown declared a state of emergency, putting all state resources at the disposal of his Office of Emergency Services. The quake was felt throughout the San Francisco Bay area.
The state, which sits along a series of seismic faults, is forecast to experience a much more powerful earthquake at some point, but scientists do not know when it might come or how strong it would measure, a geophysicist with the U.S. Geological Survey (USGS), Don Blakeman, said.
"Usually when people talk about 'The Big One,' they're talking about something in the order of a magnitude 9, which of course is tremendously more powerful" than Sunday's quake, he said.
DOWNTOWN NAPA CLOSED
Brick facades gave way in the historic section of downtown Napa, located about 50 miles north of San Francisco, and bricks fell off a second floor corner of the courthouse, which showed cracks. On the main street, masonry collapsed onto a car.
One building housing winery tasting rooms had to be closed to tourists, and the floors of many wine stores were stained red from the contents of broken wine bottles.
Tyler Paradise, general manager of Cult 24 wine bar in Napa, estimated his business lost $50,000 worth of bottles that spilled out of cabinets and littered the floor.
As dawn broke, merchants were on the streets sweeping up debris and boarding up windows.
State emergency officials said Sunday afternoon that 90 to 100 homes in Napa were "red-tagged," meaning they were not safe to enter.
Mark Ghilarducci, director of California Governor's Office of Emergency Services, said most of downtown Napa had been cordoned off as crew assessed building damage. City officials said all schools would be closed Monday so that buildings could be checked for structural damage.
Around the region, emergency crews worked to extinguish fires in mobile homes, close water main breaks, clean up broken glass and fix power outages.
By Sunday evening, about 11,000 to 15,000 people were still without power, down from 70,000 after the earthquake hit. "Right now, things are stabilizing a little bit," said Ghilarducci.
About 600 properties in Napa suffered water problems, said Napa Public Works Director Jack LaRochelle. Five crews were starting repairs at about 60 locations on Sunday, and the city had set up two water stations for residents who required water.
"You still see some water in the streets," said LaRochelle
Napa City Manager Mike Parness said it could take a full week before the city was fully restored.
"We're seeing people coming together and helping people and getting buildings back on line as soon as possible," Parness told a midday news conference.
"ROLLING BACK AND FORTH"
USGS said the epicenter of the quake was 5 miles (8 km) northwest of the town of American Canyon, on the northern edge of the San Francisco Bay.
It was the largest to hit the Bay Area since the Loma Prieta quake in 1989, which killed 63 people and caused $6 billion in property damage. That quake measured 6.9, while the famous one that leveled San Francisco in 1906 measured 7.8.
"It was long. I think it was the biggest one since I felt the 1989 quake," said Stephanie Martin, 47, a nursing assistant in Oakland, which sits just across the bay from San Francisco.
"Nothing tipped over, thank God. Rolling back and forth. Just woke us all up," she said.
Throughout Sunday, 50 to 60 small after-shocks hit the area. John Parrish, state geologist with the California Department of Conservation, said it was unlikely that a larger earthquake was yet to come but warned that the area could experience smaller after-shocks for the next couple of days.
A magnitude 6.9 earthquake struck southern Peru on Sunday, shaking the capital Lima 300 miles away but triggering no widespread damage or injuries. On Saturday a 6.6 quake hit central Chile, again with no reports of major damage. (Additional reporting by Fiona Ortiz and Robin Respaut; Writing by Peter Henderson, Dina Kyriakidou and Eric Beech; Editing by Leslie Adler and Jeremy Laurence)