A 6.1 magnitude earthquake has hit northern California. The quake struck at 3.20am local time (10.20 Irish time), according to the US Geological Survey, shaking the San Francisco and Sacramento areas.

The quake was centered nine miles south of Napa, a city roughly 30 miles north of San Francisco.

There are reports of approximately 15,000 people now without power in surrounding counties, but so far there are no reports of any serious damage.

There are no immediate reports of injury or serious damage.