Three badly hurt after quake hits northern California
The US Geological Survey said it struck at 03:20 local time (10:20 GMT) four miles (6km) north-west of the town of American Canyon, at a depth of 6.7 miles.
At least 87 people in the Napa area were taken to hospital, with three of them seriously injured.
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Hide AdCalifornia Governor Jerry Brown declared a state of emergency.
Officials in Napa said the quake had destroyed four mobile homes and caused about 50 gas main breaks and 30 leaks from water mains.
Three historic buildings in the town had been hit and two commercial buildings “severely damaged”.
Meanwhile, the Pacific Gas and Electric Company said more than 10,000 households were without power in Napa and the surrounding area.
An evacuation centre was set up in a high school gym.
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Hide AdThe tremor is the largest to shake the Bay Area since the 1989 6.9 magnitude Loma Prieta quake, the USGS said.
The tremor set off car alarms and had residents of neighbouring Sonoma County running out of their houses in the middle of the night. Power was knocked out in some areas.
The depth of the earthquake was just under seven miles, and numerous small aftershocks have occurred in the Napa wine country, the USGS said.
Oakland resident Rich Lieberman said: “It felt like a side-to-side kind of rolling sensation. Nothing violent but extremely lengthy and extremely active.”