Seismic experts at the US Geological Survey said the temblor was centred in the Pacific Ocean off the coast of northern Mexico, 72 kilometers (45 miles) southwest of San Diego at 3:28 pm (2228 GMT).

Buildings in San Diego swayed strongly when the quake hit, briefly halting a meeting at its city hall, officials said.

The quake was also felt in Los Angeles and in the desert city of Palm Springs, about 160 kilometers (100 miles) east of Los Angeles, but no immediate reports of damage were received.

"It almost knocked you out of your chair; that's how strong it was," said San Diego police Lieutenant Karen Tenney, who was on the seventh floor of the city's police headquarters building when the quake struck.

The SeaWorld theme park near San Diego immediately shut down its newest attraction, the Journey to Atlantis ride, for about an hour as a preventative measure, park information officer David Koontz said.

Initial reports from a computerised earthquake warning system registered a 4.7 quake hitting an area about 90 kilometers (55 miles) northeast of Los Angeles, but officials at the California Institute of Technology (CalTech) said the report was generated by a computer glitch.

The region, dominated by the notorious San Andreas Fault that has threatened California's urban centres for more than a century, is prone to earthquakes and is constantly on alert for seismic activity.

A 5.2 quake could cause significant damage if it were centered in an urban area, CalTech experts said.

TERRA.WIRE