Southern California was hit by its strongest earthquake in two decades on Thursday.
The epicentre of the 6.4 magnitude tremor was near the city of Ridgecrest, which is about 150 miles (240 km) north-east of Los Angeles.
Firefighters provided medical assistance and dealt with fires in and around the city on Friday.
People from the Mojave Desert to the Pacific coast reported feeling the quake, which hit on Independence Day.
There was significant damage in Ridgecrest, which lies south-west of the epicentre, local geophysicist Professor John Rundle told the BBC.
He added that it was fortunate the quake had happened far away from major population centres.
Roads were cracked and broken and power lines fell to the ground after the earthquake, which also shattered glass and cracked the walls of some homes in the region.
The Ridgecrest Regional Hospital was evacuated, the Kern County Fire Department said. The service has responded to nearly two dozen incidents ranging from medical assistance for minor injuries to fires.
The quake also struck near China Lake - the bomb testing facility of the US Navy, where weapons and aircraft are put to through their paces. One official from the facility told AFP news agency there was "substantial damage" – including fires, water leaks, and hazardous materials spills.
Brad Alexander, a spokesman for California Governor's Office of Emergency Services, said on Thursday that fire engines and search and rescue teams were going to assist in the Ridgecrest area, where he believed there were a number of buildings on fire.
"This may not be over. There could be more earthquakes happening in the area and anyone listening that's in that region should be prepared to drop, cover and hold on," he warned.
Governor of California Gavin Newsom declared an emergency for the areas affected, as concern for potential aftershocks ramped up.
Mayor of Ridgecrest Peggy Breeden said that some people had been struck by objects falling from buildings and gas lines had been broken.
"We are used to earthquakes but we're not used to this significance," she said.
Los Angeles' early warning system did not send an advance alert to many residents in the region, the LA Times reports - because the forecast did not meet the threshold of severity for Los Angeles County. In the end, the shaking was worse than expected for some people.
Stephen Sykes, who lives in Ridgecrest, was in the shower when his house started to shake.
"The whole house shook violently and we both ran out into the street. This went on for about 10 to 15 seconds, we were really scared," he told the BBC.
"Currently we are getting ready in case there's another one. We are moving items onto the floor and have turned off the gas supply. We will probably sleep outside tonight," he added.
The earthquake was reportedly felt as far as Las Vegas in Nevada. There have been several smaller aftershocks.
President Donald Trump tweeted that the situation was under control.
Lucy Jones, a seismologist with the US Geological Survey, told reporters the epicentre was in a relatively uninhabited area.
She said there would likely be a number of aftershocks, some powerful.
One man tweeted images from inside a supermarket in Ridgecrest, which has a population of about 28,000 people, showing the aisle floors covered with fallen items.
