Southern California was hit by its largest earthquake in two decades Friday, a 7.1-magnitude tremor that rattled residents who were already reeling from another strong quake a day earlier.
Emergency workers and security forces were being dispatched early Saturday to the epicenter of the shallow earthquake in a remote and sparsely populated area around 150 miles (240 kilometers) northeast of Los Angeles, where it was also felt.
No deaths or serious injuries had been reported late Friday evening, but there were reports of building collapses and power outages in the town of Trona, California Office of Emergency Services director Mark Ghilarducci said.
There were "significant reports" of fires caused by gas leaks, as well as breaks to power, water and communications lines in the region, he told a press conference.
California Governor Gavin Newsom said he had requested emergency federal assistance from the White House, and state resources have been activated at their "highest level."
Newsom later declared a state of emergency for San Bernardino County, expanding on an earlier announcement covering Kern County, near the epicenter of both the quakes this week.
A joint task force including around 200 security personnel as well as helicopters and cargo aircraft was being deployed, National Guard Major General David Baldwin said.
San Bernardino fire department spokesman Jeremy Kern told CNN there were "no active searches ongoing" for trapped casualties.
The quake was 11 times stronger than the 6.4-magnitude quake "foreshock" the previous day, according to the United States Geological Survey.
The two major quakes, along with multiple aftershocks, have revived fears of the "Big One" -- a powerful tremor along the San Andreas Fault that could devastate major cities in Southern California.
"This is an earthquake sequence. These earthquakes are related," said Caltech seismologist Lucy Jones.
There was a 10 per cent chance of Friday's quake being followed by another magnitude 7.0 or higher quake in the next week, she added.
- 'Scary' -
In Kern County, where the quake struck near the town of Ridgecrest, some 1,800 residents were without power, fire department chief David Witt said.
"As for injuries reported, nothing but minor injuries and such as cuts and bruises, by the grace of god," he said.
At least two fires broke out in the area, county supervisor Mick Gleason said, with dozens of fire trucks dispatched.
Numerous gas leaks were reported near the epicenter, including the towns of Trona and Argus.
"Firefighters have secured leaks where possible and evacuated residents from homes with leaks that cannot be secured," the San Bernardino fire department tweeted.
In Los Angeles, the fire department deployed vehicles and helicopters, and reported fallen power lines and localized electricity outages.
But Mayor Eric Garcetti said there were "no reports of serious damage" reported in the city.
"We are sending an Urban Search and Rescue Task Force Team to Kern County to help with the damage closer to the epicenter," he wrote on Twitter.
Numerous visitors to Disneyland in Anaheim reported on Twitter that rides were shut for safety inspections after the quake.
Patrons at movie theaters in the Los Angeles area evacuated due to the quake.
"Everyone remained calm as the theater began to shake and then the shaking got stronger. We all headed to exits and down the stairs. No panic but one woman sobbing. This one was scary," wrote NBC journalist Lester Holt on Twitter.
No damage was reported at Los Angeles airport following inspections.
In Las Vegas, 150 miles east of the quake, an NBA summer league game was postponed when the tremor hit, causing the scoreboard and several overhead speakers to sway.
- Aftershocks -
The earthquake was the largest in southern California since 1999 when a 7.1-magnitude quake struck the Twentynine Palms Marine Corps base, according to The Los Angeles Times.
The tremor sent Ridgecrest residents fleeing outside for safety as aftershocks continued, with one woman saying she was "not comfortable" about heading back inside for the night.
The shaking stops "for a minute, and then it starts rolling again... it's pretty bizarre. But now at the moment, I'm not comfortable inside," said Jessica Kormelink.
"I was actually in the car with my mom. And it just started bouncing up," Jessica Weston, a journalist at the Ridgecrest Daily Independent, told CNN.
Relief efforts in the area benefited from the arrival of major reinforcements that arrived Thursday afternoon, intended to counter a new potentially destructive earthquake.