Rick Ruiz (L) and Tyler Paradise gather broken wine bottles from the floor of their Cult Following Wine Bar after an earthquake in Napa, California August 24, 2014. The 6.0 earthquake rocked wine county north of San Francisco early Sunday, injuring dozens of people, damaging historical buildings, setting some homes on fire and causing power outages around the picturesque town of Napa. [Photo/Agencies]

NAPA, Calif. - A 6.0 magnitude earthquake rocked wine country north of San Francisco early on Sunday, injuring dozens of people, damaging historic buildings, setting some homes on fire and causing power outages around the picturesque town of Napa.

The biggest quake in the region in 25 years jolted many residents out of bed when it hit at 3:20 a.m. (1020 GMT), centered 6 miles (10 km) south of the City of Napa.

CNN put the number of injuries as 120.

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.

Queen of the Valley hospital said it had treated 89 patients.

There were no reports of any fatalities but the quake shook up residents, said Barry Martin, community outreach coordinator for the City of Napa, which has a population of 77,000.

"This was a pretty big jolt in Napa, but it certainly is not The Big One," Martin added in comments to local television, referring to fears Californians have of a catastrophic quake.

California, 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 exactly when it will come or how strong it will be, USGS geophysicist Don Blakeman said.

"Usually when people talk about 'The Big One,' they're talking about something on the order of a magnitude 9, which of course is tremendously more powerful" than Sunday's quake, he said.

California Governor Jerry Brown declared a state of emergency, putting all state resources at the disposal of his Office of Emergency Services.

Most damage appeared centered around Napa, a famous wine-producing region and a major tourist destination in northern California.

One hard-hit 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. They were shaken out of their holding cabinets and littered the floor.