A powerful magnitude 6.4 earthquake that struck southern California shook buildings from Los Angeles to Las Vegas causing millions of dollars in daamge.

Dozens of aftershocks have already been felt after the tremor hit Friday morning (Australian time) near the city of Ridgecrest, about 175km northeast of Los Angeles.

It was the strongest quake to hit the region in 20 years.

Some injuries and two house fires were reported in the town of Ridgecrest which has a population of 28,000.

Emergency crews were also dealing with small vegetation fires, gas leaks and reports of cracked roads, said Kern County Fire Chief David Witt.

He said 15 patients were evacuated from the Ridgecrest Regional Hospital as a precaution and out of concern for aftershocks.

Kern County District Supervisor Mick Gleason told CNN there were some structural issues with the hospital and some patients had to be moved from one ward to another and that others were taken to a neighbouring building.

Ridgecrest Mayor Peggy Breeden said that utility workers were assessing broken gas lines and turning off gas where necessary.

The local senior centre was holding a July 4th event when the quake hit and everyone made it out shaken up but without injuries, she said.

A series of aftershocks included a 4.5 magnitude tremor, according to the United States Geological Survey.

“It almost gave me a heart attack,” said Cora Burke, a waitress at Midway Cafe in Ridgecrest, of the big jolt.

It’s just a rolling feeling inside the building, inside the cafe and all of a sudden everything started falling off the shelf, glasses, the refrigerator and everything in the small refrigerator fell over.”

Video posted online of a liquor store in Ridgecrest showed the aisles filled with broken wine and liquor bottles, knocked down boxes and other groceries strewn on the floor. Flames were seen shooting out of one home in the community.

Lucy Jones, a seismologist with the California Institute of Technology’s seismology lab, said the earthquake was the strongest since a 7.1 quake struck in the area on October 16, 1999.

She said vigorous aftershocks were occurring and that she wouldn’t be surprised if a magnitude 5 quake hit but that they were striking in a remote area, sparsely populated area.

“This is an isolated enough location that that’s going to greatly reduce the damage,” she said.

The quake was detected by California’s new ShakeAlert system and it provided 48 seconds of warning to the seismology lab well before the shaking arrived at Caltech in the Los Angeles suburb of Pasadena.

“It’s certain that this area is going to be shaking a lot today and some of those aftershocks will probably exceed magnitude 5,” Ms Jones said.

Footage from Ridgecrest showed firefighters hosing down flames rising from homes.

A state of emergency has been declared in Ridgecrest. Photo: CNN

Busy Highway 178 had a 4-inch (10cm) crack, San Bernardino County Fire spokesman Jeremy Kern said.

Filmmaker Ava DuVernay tweeted: “Been living in Los Angeles all my life. That was the longest earthquake I’ve ever experienced … Is this the big one?”

https://twitter.com/ava/status/1146835415707467777

Video posted online of a liquor store in Ridgecrest showed the aisles filled with broken wine and liquor bottles, knocked down boxes and other groceries strewn on the floor. There was at least one house on fire in the city.

My dads liquor store in Ridgecrest (11 miles from the earthquake) 🥴 pic.twitter.com/4RC0mY3eha

— Zomo (@zomo_abd) July 4, 2019

Ms Jones said the earthquake was the strongest to hit Southern California in 20 years.

-with agencies