Preliminary information from the U.S. Geological Survey estimated the quake at magnitude 5.8, centered 29 miles southeast of downtown Los Angeles near Chino Hills in San Bernardino County. Ten aftershocks occurred in the next dozen minutes, including three estimated at 3.8, and the U.S. Geological Survey estimated the quake was about 8 miles below the earth's surface.
Los Angeles Fire Department spokesman Brian Humphrey said there were no immediate reports of damage or injury in Los Angeles. San Bernardino County fire dispatch also had no immediate reports of damage.
The quake struck at 11:42 a.m. PDT. Buildings swayed in downtown Los Angeles for several seconds.
Workers quickly evacuated some office buildings.
"It was dramatic. The whole building moved and it lasted for a while," said Los Angeles County sheriff's spokesman Steve Whitmore, who was in the sheriff's suburban Monterey Park headquarters east of Los Angeles.
In Orange County, about 2000 detectives were attending gang conference at a Marriott hotel in Anaheim when a violent jolt shook the main conference room.
Mike Willever, who was at the hotel, said, "First we heard the ceiling shaking, then the chandelier started to shake, then there was a sudden movement of the floor."
Chris Watkins, from San Diego, said he previously felt several earthquakes, but "that was one of the worst ones."
Delegates and guests at a cluster of hotels near the Disneyland resort spilled into the streets immediately after the quake.
The 1994 Northridge earthquake under Los Angeles' San Fernando Valley was magnitude 6.7. It killed 72 people, injured more than 9,000 and caused $25 billion in damage in the metropolitan area.
The damage created by an earthquake depends greatly on where it hits. A 7.1 quake -- much stronger than Northridge -- hit the Mojave Desert in 1999 but caused only a few injuries and no deaths.
California is one of the world's most seismically active regions. More than 300 faults crisscross the state, which sits atop two of Earth's major tectonic plates, the Pacific and North American plates. About 10,000 quakes each year rattle Southern California alone, although most of them are too small to be felt.
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