An earthquake rocked southern California last night, killing three people and sending tremors from Los Angeles to San Francisco.

With a magnitude of 6.5 on the Richter scale, according to the US Geological Survey, its epicentre was the northern coastal town of Cambria, 185 miles north-west of Los Angeles, where residents felt a gentle, sustained rolling. In Paso Robles, 20 miles east of the epicentre, the roof of a clock tower was hurled into the street, crushing a row of parked cars. The bodies of three people were pulled from the rubble outside a row of shops.

In San Francisco, the quake rocked the 20-storey federal courthouse, with its upper floors swaying for about 30 seconds.

It struck a series of faults that run parallel to the San Andreas fault, according to Lucy Jones, the scientist in charge of the US Geological Survey office in Pasadena. "It's luckily on the coast; there is not very much nearby," she said.

The epicentre was near San Simeon, home to newspaper publisher William Randolph Hearst's castle, which was evacuated after the quake.

Tad Weber, the managing editor of the Tribune in San Luis Obispo, about 30 miles south-east of Cambria, said he was in a meeting when "all of a sudden there was a jolting and we look up and see the building swaying. I dove under a desk to wait it out".

Sheriff's sergeant Pete Hodgkin in San Luis Obispo county said: "It felt like a big one, like the San Francisco earthquake years ago. We're on emergency power here."

A quake with a magnitude of six can cause severe damage in a populated area, though damage is often much less in places with strong building codes.