(CNN) - Aftershocks kept rolling across Southern California on Friday morning, with one measuring 5.4 reported northeast of Ridgecrest, the US Geological Survey said.
That temblor, recorded at 4:07 a.m. (7:07 a.m. ET) Friday, was the strongest of more than 170 aftershocks that followed Thursday's powerful 6.4-magnitude earthquake, the USGS said.
Thursday's earthquake -- centered near Ridgecrest, 150 miles north of Los Angeles -- was the strongest to hit Southern California in nearly 20 years, prompting one city's mayor and later the governor to declare a state of emergency for the area.
Thursday's quake was like being in a movie, Ridgecrest resident Sara Baird said.
"Everything shakes. The whole ground shakes beneath you, the whole house. Everything fell in my kitchen, it's still on the floor," Baird told CNN affiliateKABC.
The US Geological Survey said there's a 20% chance of an earthquake of magnitude 6 or higher occurring in the next week and an 80% chance of a magnitude 5 or higher quake hitting the state.
But a larger quake isn't as likely, the agency said.
"While it is always possible for large quakes to trigger an even larger quake, most do not," the agency said. "It's generally not possible to determine whether a given quake will turn out to be a 'foreshock' of a larger one."
The chance of another earthquake equally as or more powerful hitting in the next week is only 9%, the USGS said.
An earthquake as powerful as this week's will produce an aftershock as large as a 5.4 magnitude, the agency said, and 10 aftershocks with magnitude 4.4 or higher.
Over the next few days, smaller earthquakes are likely, with up to 700 aftershocks of magnitude 3 or higher, according to the USGS.
Gas leaks, fires, cracked roads in earthquake's epicenter
PAGER -- the USGS's system for estimating fatality and economic loss impact after earthquakes -- estimates there will be between $10 million to $100 million in losses following Thursday's quake.
The rattle was felt from Las Vegas to Orange County and cities throughout California saw varying degrees of damage.
Ridgecrest Mayor Peggy Breeden declared a state of emergency, saying there were five fires and broken gas lines across the city of 28,000. Ridgecrest Regional Hospital was evacuated and about 15 patients from the emergency room were taken to other hospitals.
One resident, Kimberly Washburn, was directing a children's July 4th program when the building began to shake, startling the 65 children on stage, who began screaming.
"It was terrifying," she said.
One boy was injured when something fell on his foot, but Washburn said they were blessed that more weren't hurt. After they evacuated, a wall fell behind where the children had been performing, she said.
In Kern County, the earthquake's epicenter, the fire department responded to more than 20 incidents relating to the earthquake and aftershocks, including fires and medical emergencies, the department said.
Over 160 emergency calls in the area caused an "extreme backlog" after the quake, Kern County Fire Chief David Witt said Thursday.
"We have more calls than we have people," Witt told reporters.
California Gov. Gavin Newsom approved an emergency proclamation for the county to address the earthquake and aftershocks.
Multiple areas felt the shake
In Los Angeles, where many felt the ground rolling, Disneyland officials temporarily shut down rides.
In San Bernardino, east of Los Angeles, the fire department reported buildings sustained minor cracks, water mains broke and several power lines were down.
A 4-inch crack opened up in Highway 178, according to San Bernardino County Fire spokesman Jeremy Kern.
Trona, an unincorporated community, "sustained varying degrees of damage" but no injuries were reported, according to San Bernardino County Fire's verified Twitter account.
The strongest quakes in Southern California
The last time Southern California saw such a forceful quake was nearly 20 years ago, when the 7.1 Hector Mine quake shook the Mojave Desert.
That quake struck in the early morning hours of October 16, 1999 and people from Southern California to Arizona and Nevada felt the tremor. But because the quake was centered in a remote region, it caused "relatively negligible damage," the Southern California Earthquake Data Center said.
In 1994, Los Angeles' San Fernando Valley was struck by a deadly 6.7 magnitude earthquake that killed at least 57 people and injured more than 7,000, according to the USGS.
"The earthquake had immense impact on people and structures because it was centered directly beneath a heavily populated and built-up urban region," the USGS said.
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