Emergency crews in Southern California are tackling a number of fires and gas leaks following a major earthquake that damaged buildings, ruptured gas lines and sparked fires near the remote epicenter of the temblor.

The epicentre of the quake, which was the second in the area this week, was located around 200km north of Los Angeles. 

The tremor rocked the Mojave Desert town of Ridgecrest south of Death Valley National Park as darkness fell last night, jolting the area with eight times more force than the 6.4 quake that struck the same area 34 hours earlier.

California Governor Gavin Newsom requested federal assistance and placed the state Office of Emergency Services (OES) on its highest alert.

"We have significant reports of fires, structural fires, mostly as a result of gas leaks or gas line breaks," OES Director Mark Ghilarducci told a late-night news conference yesterday.

Violent shaking also caused water main breaks and knocked out power and communications to parts of Ridgecrest, a city of about 27,000 that lies about 202km northeast of Los Angeles.

No fatalities or serious injuries were reported from either quake, police said. But Mr Ghilarducci said the full extent of damage would not be known before daybreak.

"This was a very large earthquake, and we also know there's going to be a series of aftershocks as a result of the main quake," he said, adding his agency faced a "challenge" getting needed resources to the isolated quake zone. 

"This is not going to be something that's going to be over right away."

Overnight, about six hours after the main quake, the town centre of Ridgecrest was quiet, except for the occasional rumble of aftershocks. 

Some residents could be seen sitting on lawn chairs in the darkness outside. The garage doors of many homes were left open with a car parked on the driveway.

Yesterday's earthquake was widely felt across Southern California, including greater Los Angeles, where shaking in some areas lasted about 40 seconds. Low-level rumbling extended as far north as the San Francisco Bay area and beyond to Reno, Nevada, and as far east as Phoenix, Arizona.

Seismologists said the initial quake on Thursday, and dozens of smaller ones that followed it, proved to be foreshocks to yesterday's much larger temblor, which now ranks as Southern California's most powerful since a 7.1 quake that struck near a US Marine Corps base in the Mojave Desert in 1999.

The US Geological Survey said yesterday's big quake was immediately followed by at least 16 aftershocks of magnitude 4 or greater, and warned of a 50% chance of another magnitude 6 quake in the days ahead. 

Geologists put the chance of another magnitude 7 tremor at 10% over the next week.

A rockslide closed State Road 178 in Kern County, and video footage posted on Twitter showed a stretch of road had buckled.

The last major destructive quake to hit Southern California was the 6.7 magnitude Northridge quake in 1994, which struck a densely populated area of Los Angeles. It killed 57 people and caused billions of dollars in property damage.

The comparatively limited extent of damage from yesterday's quake, packing greater force than the Northridge event, was a function of its location in a remote, less developed area.

Its ground motion, however, startled seismically-jaded Southern Californians over a wide region.

Pools in Los Angeles sloshed wildly, and TV cameras at major league baseball's Dodger Stadium were shaking as they filmed the night game between the Los Angeles Dodgers and San Diego Padres.

A television anchorwoman ducked under her desk in midst of a local newscast as shouts of "get under a desk" were heard in the background.