Earthquake Struck California

A 6.0 magnitude earthquake shook California's Napa and Sonoma counties three people have been critically injured.

The earthquake was felt as far north as San Francisco, set off car alarms and caused residents to run out of their homes in the middle of the night.

Some 70 people received minor injuries after the quake struck at 3.20am (10.20am GMT) at a depth of seven miles, and 40 miles (64 kilometers) northeast of San Francisco,

6.0 Earthquake Rattles Northern California

A reporter surveys the scene of a building collapse in Napa

Pictures posted on Twitter showed firefighters putting out a blaze at a mobile home park in Napa Valley and piles of rubble and masonry lying in the street which had fallen from buildings.

A 2.6 magnitude aftershock hit half an hour later and US Geological Survey (USGS) expert Jessica Turner told KCBS radio that aftershocks of up to 5.0 are likely in the coming week.

The shocks will be examined by geologists to determine whether the quake happened on a geological fault line.

The USGS added there was a "low likelihood for casualties," but issued an "orange alert" for possible damage, which means "significant damage is likely and the disaster is potentially widespread."

Californian police closed several roads which suffered significant damage and warned drivers to take extra while crossing an intersection in Napa Valley strewn with bricks after a building partially collapsed.

6.0 Earthquake Rattles Northern California

People wearing bathrobes walk down a street in Napa

Engineers were dispatched to assess the damage and restore power to some 50,000 residents in Napa and Sonoma who suffered a blackout.

Randy Baldwin, a USGS geophysicist, said the tremor was potentially damaging because it was close to populated areas.

"It is the strongest quake in a 60-mile (100-km) radius from the epicenter of this quake in several decades," he said.