A 6.4 magnitude earthquake rattled Southern California on Thursday and officials said it was the largest to hit the region in 20 years. The quake struck near the city of Ridgecrest, which is located about 160 miles northeast of Los Angeles.

Some injuries were reported in Ridgecrest, authorities said, but the extent is currently unclear. A city in the hospital was evacuated and officials are assessing structural damage to the building.

The United States Geological Survey said the quake struck at 10:33 a.m. PT. The earthquake was initially given a magnitude of 6.6, but was later revised to 6.4. The quake was felt more than 150 miles away in Los Angeles, but no damage was reported.

This was the largest quake to hit Southern California since 1999 and an eerie reminder of the 1994 Northridge quake. The magnitude 6.6 earthquake killed at least 57 people and caused billions of dollars in damage.

The city of Los Angeles has lowered the threshold on its earthquake app following public outcry, CBS Los Angeles reported. Residents were not alerted to the quake Thursday via Shakealert L.A. because it only registered at magnitude 4.5 in Los Angeles county.

"We hear you and will lower the alert threshold with @USGS_ShakeAlert," the City of Los Angeles tweeted.

The city of Los Angeles announced it would be working with the U.S. Geological Survey on the update to its app.

A state of emergency has been issued for Ridgecrest by local officials. California Gov. Gavin Newsom also declared a state of emergency for Kern County, where Ridgecrest is located. The declaration allows the state to help the region with emergency aid and recovery efforts.

Ridgecrest Mayor Peggy Breeden praised Newsom's decision. She also noted at a news conference that other nearby governments have offered to help the recovery effort.

Injuries reported in Ridgecrest

There were some injuries, but authorities are not saying to what extent right now. No deaths were reported and the hospital in Ridgecrest is not dealing with any earthquake related injuries. They did evacuate patients and need to assess structural and other damage.

Dr. Lucy Jones, a seismologist with the United States Geological Survey, said there has already been a high number of aftershocks following the quake. "I think we have already had probably an excess of 20 3.5 [magnitude aftershocks]," Jones said in a news conference.

"I would expect that there will continue to be magnitude 3s every few minutes, as there have been since this earthquake happened and that as those many 3s come through, we're going to have several 4s," Jones continued.

She said several minutes before the news conference, she had logged a 4.1 magnitude aftershock.

"We will be continuing to have lots of aftershocks," she said. "There is a 1 in 20 chance that this location could have an even bigger quake in the next few days."

House catches fire following earthquake

A massive house fire in Ridgecrest was caught on video following the 6.4 magnitude earthquake. It's unclear what caused the blaze.

The earthquake was followed by dozens of aftershocks in Ridgecrest and Searles Valley, measuring anywhere from magnitude 2.9 to 4.2, according to CBS Los Angeles.

The earthquake is the largest in 20 yearsThe 6.4 magnitude earthquake is the largest to hit Southern California since 1999, Dr. Lucy Jones, a seismologist with the United States Geological Survey said Thursday.

Source: CBS News