Los Angeles is in "earthquake mode" after a 5.3 magnitude quake struck off the coast of Southern California.
The quake's epicentre was around 60km southwest of Ventura, near the Channel Islands, at 12.29pm on Thursday (local time), the US Geological Survey (USGS) said.
It was the strongest tremor to hit the area in four years, fuelling fears the "big one" was coming and placing emergency services on high alert.
The jolt sent the Los Angeles Fire Department (LAFD) into "earthquake mode", deploying firefighters across the city to check over buildings, power lines and dams.
The quake was viewed as an ideal opportunity for emergency services to prepare for a major earthquake.
The USGS recently predicted that California has a 46 per cent chance of a 7.5 magnitude or higher quake within the next 30 years.
Experts predict an earthquake of 7.8 — three times as powerful as the one that hit in 1994 — would leave at least 50,000 injured.
Shaking was felt all along the coast, from the San Luis Obispo area to the north to San Clemente in the south, USGS reported.
Many of the more than 300 day visitors and campers who were on Santa Rosa, Santa Cruz and Anacapa islands when the temblor struck reported feeling a jolt and rolling motions, according to Yvonne Menard, a spokeswoman for the Channel Islands National Park.
A couple of bricks fell off a chimney structure on a Nature Conservancy property on Santa Cruz Island, but beyond that there were no injuries on any of the islands, Ms Menard told KTLA.
No evacuations were ordered.
On social media, people across the Southern California region also reported feeling the quake, with many describing it as "rolling".
One woman said the quake's "rolling motion" caused walls to creak and items to swing in Torrance.
For those working in high-rise buildings, the shaking was more intensely felt.
"It lasted about a minute and it was pretty scary," Gary Daugenti, who was on the 12th floor of an office building when the shaking began, told KTLA.
"It started rolling but it got a little bit more violent as it went on, but it didn't get to the point where it was a violent shake."
Aftershocks were felt as far away as San Jacinto and central Orange County.
Some people in the Los Angeles area received about a 10-second warning before the shaking hit thanks to the state's earthquake early warning system, according to seismologists at the California Institute of Technology.
The warning was long "enough for us to puzzle about it before the shaking hit", Southern California Earthquake Center Director John Vidale told the Los Angeles Times.
According to Jones, a quake this large hasn't occurred in the region in several years, a period she called "quiet".
"It's a regular sort of earthquake that we expect somewhere in Southern California," Jones told KTLA.
"Magnitude 5.3 is a size that happens on average about once a year in Southern California."
Ventura County Fire Department Captain Steve Swindle told KTLA he was at the agency's headquarters in Camarillo when the earthquake hit and felt it.
Capt Swindle said that during a tremor, officials at stations put out their apparatuses and fire engines so they can be prepared to respond in the event of an aftershock.
"So far, thankfully, there hasn't been any damage reported out of this," he said.
The fire chief advised residents of Ventura County to be prepared for more possible tremors.
"It is Southern California, we are earthquake country. We know that it's coming," he said.
"Being prepared is always your best bet to help yourself."