A screen print of the US Geological Survey

The US Geological Survey has withdrawn a report saying that a magnitude 5.0 earthquake has hit northern California.

It said the report was issued because scientists had not reviewed an automated alert, a geophysicist was quoted as saying by Reuters agency.

Paul Caruso told the agency that the tremor had not happened.

The USGS had earlier reported on its website that a magnitude 5.0 earthquake struck north-east of Napa at a depth of 3.1 miles (5km).

The report was withdrawn from the website soon after publication.

The USGS later said a computer at its Berkeley station mistakenly concluded that northern California had been hit by the quake, the Associated Press reported.

It quoted Richard Buckmaster, a geophysicist at the USGS’s National Earthquake Reporting Center, as saying officials were trying to establish why the computer generated the "dubious and erroneous" alert.

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