The earthquake damaged this building in Napa, California. Photo: Getty Images
San Francisco: A strong 6.0-magnitude earthquake jolted California early on Sunday morning, the US Geological Survey (USGS) said, though there were no immediate reports of deaths or serious damage.
The earthquake, the largest in the region for 25 years, struck at 3.20am near American Canyon, 60 kilometres north-east of San Francisco, USGS said.
The USGS said there was a "low likelihood" of casualties but issued an "orange alert" for possible damage, a rating which means "significant damage is likely and the disaster is potentially widespread".
The earthquake shattered the glass of shop windows in Napa, California. Photo: Getty Images
An aftershock of 2.6-magnitude hit about 30 minutes afterwards, it said.
USGS expert Jessica Turner told KCBS radio that aftershocks of up to 5.0 are likely in the next week.
Local CBS news said several fires had broken out in Napa, about 10 kilometres from the earthquake's epicentre, which is famous as a wine-growing region.
Damage from the earthquake was widespread, but not major, authorities said. Photo: Lyall Davenport/AP
The power was out in Napa as well as in other towns and cities nearby, affecting more than 10,000 households, according to the Pacific Gas and Electric Company.
Early reports suggested some damage close to the earthquake's epicentre, but no reports of anything major.
It said it had sent crews out to assess the damage and restore power, and estimated electricity would be back up within several hours.
The California Highway Patrol in the San Francisco Bay Area tweeted that it was "checking over crossings and bridges for obvious signs of structural integrity," and asked residents to report any signs of problems.
They closed a bridge near Vallejo on Highway 37 while inspecting for possible damage, KCBS reported.
"Oh I felt it. When I woke up I was lying on the floor. It kicked me out of bed," said Keith, a man who lives in Napa and who wished to be identified only by his first name.
"The house is a mess, everything is out of the cabinets in the kitchen. Dressers tipped over."
Residents in the area, including as far away as San Francisco and Davis, quickly took to Twitter.
One user, Tyson Winter, wrote: "Shook violently here in Napa. Power's out."
Ann Marie Christy wrote that her mother, also in Napa, said the shaking "was very violent with a lot of broken glass".
And in San Francisco, Om Malik posted "Damn, woke me up. Was super long."
Further north, Tim Kerbavaz tweeted: "Felt it in Davis too. Quite long."
Reporters in Oakland felt the quake as a long, low swell that shook gently for several seconds.
The earthquake was the largest to hit the Bay area since the Loma Prieto earthquake in 1989.
"It is the strongest quake in a 60-mile [100-kilometre] radius from the epicentre of this quake in several decades," USGS geophysicist Randy Baldwin said.
"It was a shallow quake and there are lots of aftershocks," he said, adding most were about magnitude 2 range.