Donald Trump has been asked by California's governor to declare a state of emergency after a 7.1 magnitude earthquake struck the state, cracking roads, triggering building fires and causing a number of injuries.

The quake, which followed a 6.4 magnitude foreshock on 4 July, was the biggest the region has suffered in 20 years and was felt as far away as Mexico and Las Vegas after it struck on Friday evening.

It was centred about 150 miles northeast of Los Angeles near the town of Ridgecrest in the Mojave Desert - as was the Independence Day tremor - and was followed by a series of aftershocks, which seismologists warned could last for days, or even weeks.

The area in and around Ridgecrest, already trying to recover from Thursday's foreshock, took the brunt of damage. Several thousand people were without power, and there were reports of cracked buildings.

Mark Ghillarducci, director of the California Office of Emergency Services, said there were "significant reports of structure fires, mostly as a result of gas leaks or gas line breaks throughout the city".

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He also said there was a report of a building collapse in tiny Trona and that there could be even more serious damage to the region that will not be known until first light on Saturday.

There were reports of trailers burning at a mobile home and State Route 178 in Kern County was closed by a rockslide and roadway damage.

Kern County fire chief David Witt said there had been a lot of ambulance calls but no reported fatalities.

For the second time in as many days, Ridgecrest Regional Hospital wheeled patients out of the building, some still hooked to IVs, CNN reported.

In downtown Los Angeles, 150 miles away, offices in skyscrapers rolled and rocked for at least 30 seconds.

Andrew Lippman, who lives in suburban South Pasadena, was sitting outside and reading the paper when Friday's quake hit and calculated it lasted 45 seconds.

"I could see power lines swaying," he said.

Disneyland in Orange County and Six Flags Magic Mountain in Santa Clarita closed their rides.

An NBA Summer League game in Las Vegas was stopped after the quake. Speakers over the court at the Thomas & Mack Center continued swaying more than 10 minutes after the quake.

The quake rattled Dodger Stadium in the fourth inning of the team's game against the San Diego Padres, when Los Angeles Dodgers second baseman Enrique Hernandez was batting. It did not appear to affect him or Padres pitcher Eric Lauer.

However, it was obvious to viewers of the SportsNet LA broadcast when the TV picture bounced up and down. Some fans in the upper deck appeared to leave their seats and move to a concourse at the top of the stadium.

There is about a 1-in-10 chance that another 7.0 magnitude quake could hit within the next week, said Lucy Jones, a seismologist at the California Institute of Technology and a former science adviser at the US Geological Survey.

California earthquake: Powerful 6.4 magnitude quake hits near city of Ridgecrest

The chance of a 5.0 magnitude quake "is approaching certainty", she added, with aftershocks from the main quake potentially continuing for years.

However, the quake was unlikely to affect fault lines outside of the area, she said, noting that the gigantic San Andreas Fault was far away.

"These earthquakes are related," Ms Jones said, adding that the new quake probably ruptured along about 25 miles of fault line and was part of a continuing sequence.

Governor Gavin Newsom activated the state Office of Emergency Services operations centre "to its highest level" and announced he had requested Mr Trump issue an emergency declaration so the state could receive federal aid.

The city of Los Angeles is planning to reduce the threshold for public notifications by its earthquake early warning app, but officials say it was in the works before southern California's initial earthquake on Thursday.

The ShakeAlert LA app was designed to notify users of magnitudes of 5.0 or greater and when a separate intensity scale predicts potentially damaging shaking.

Robert de Groot of the US Geological Survey says lowering the magnitude to 4.5 was already being worked on and had been discussed with LA as recently as Wednesday.