What to Know The quake was the largest to hit the region since 1999.

Most damage was reported near Ridgecrest, where a state of emergency was declared.

Many aftershocks should be expected in the coming days, experts from Caltech say.

A magnitude-6.4 earthquake rattled Southern California Thursday morning, with residents reporting feeling it from the high desert to the coast.

Southern California's largest magnitude earthquake in the last 20 years was centered in Searles Valley, near the high desert town of Ridgecrest about 150 miles north of Los Angeles. It was reported at 10:33 a.m. and followed by a swarm of aftershocks ranging from magnitude 2.8 to magnitude 4.2.

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A state of emergency was later declared in Ridgecrest after some damage and widespread power outages were reported. Injuries and two house fires were reported the town 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.

There is a high likelihood of an aftershock larger than a 5.0 magnitude Thursday afternoon among the expected swarm of aftershocks, according to Dr. Lucy Jones, a prominent seismologist and Southern California earthquake expert who works with the USGS and Caltech.

The earthquake was 5.4 miles deep, which is considered moderate. The closer to the surface an earthquake is, the more it is usually felt.

"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."

This #earthquake was 5.4 miles deep, a moderate depth. The closer it is to the surface the more it is felt... usually. #NBCLA pic.twitter.com/WW6CZ07qvk — Anthony Yanez (@AnthonyNBCLA) July 4, 2019

There were widespread reports of heavy shaking near the temblor's epicenter outside of Ridgecrest. Ridgecrest Mayor Peggy Breeden said that utility workers were assessing broken gas lines and turning off gas where necessary.

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

"Oh, my goodness, there's another one (quake) right now," Breeden said on live television as an aftershock struck.

President Donald Trump said he was fully briefed on the earthquake and that it "all seems to be very much under control!"

Security cameras caught an unusual sight outside a Ridgecrest home. Parked cars and a pickup were jostled around by the powerful magnitude-6.4 Independence Day earthquake.

Evacuations were underway after noon at Ridgecrest Regional Hospital, according to the Kern County Fire Department. The hospital said the emergency room and urgent care remained open, but some patients were being transferred until the structural integrity of the building could be assessed.

Several apartment buildings were also evacuated, accoring to the Kern County Sheriff's Office. Stores were in shambles and widespread power outages were also reported. Some roads cracked apart.

Members of the Los Angeles County Fire Department were headed to Kern County to assist, according to a tweet from its main account.

There were no immediate reports of damage in the Los Angeles area.

Full shot of my dads store in Ridgecrest 😓 pic.twitter.com/WPXnHxx00m — Joe tiessan (@joe_tiessan) July 4, 2019

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The quake was in the same area that was struck by a magnitude-5.4 quake in 1995. That Aug. 17 earthquake, centered north of Ridgecrest, was followed by more than 2,500 aftershocks during the following five weeks.

Missing Attachment What to know about faults, aftershocks and more following the magnitude-6.4 earthquake near Ridgecrest. Anthony Yanez reports for the NBC4 News at 6 p.m. on July 4, 2019.

On Sept. 20 that same year, a second large earthquake struck the region. At magnitude-5.8, it was likely on the same fault system as the earlier quake. More than 1,900 aftershocks followed the September earthquake.

In October 1999, one of the largest earthquakes recorded in Southern California was centered in the region. The magnitude-7.1 Hector Mine quake produced shaking throughout SoCal and in parts of Arizona to Nevada from its epicenter in the Mojave Desert. It was in such a remote location that it was named after an open quarry pit and caused little damage, aside from a surface rupture in the Twentynine Palms Marine Base.

Missing Attachment The ceiling of the business collapsed in the magnitude-6.4 earthquake. Darsha Philips reports for the NBC4 News on Thursday July 4, 2019.

"This has been an extremely quiet abnormal time," said Lucy Jones, a seismologist with the California Institute of Technology's seismology lab. "This type of earthquake is much more normal... The long term average is probably once every five or 10 years somewhere in Southern California."

People across Southern California were quick to turn to social media to share their earthquake experience:

Okk that earthquake freaked me out. — Therese Anne (@_hellotherese) July 4, 2019

My dads liquor store in Ridgecrest (11 miles from the earthquake) 🥴 pic.twitter.com/4RC0mY3eha — Zomo (@zomo_abd) July 4, 2019