At least 120 people were treated at hospital and a state of emergency was declared in the city of Napa, after California was shaken by a 6.0 magnitude earthquake.

Local officials had to set up a triage tent at the Queen of the Valley Medical Center in Napa to handle the influx of the people injured in the earthquake, AP reports. According to hospital's CEO Walt Mickens, most of the injured had cuts, bumps and bruises. Three people were also admitted with broken bones, and two for heart attacks.

The 6.0 quake struck at 3:20 am (10:20 GMT), the US Geological Survey said. Its epicenter was 6 kilometers from American Canyon and 9 kilometers from the city of Napa, at a depth of 10.8 kilometers from the surface.

Residents of the cities of San Francisco, some 40 miles away, and Davis, just over 70 miles away, quickly took to Twitter reporting feeling the quake.

Earthquake just now in San Francisco. Good shaker had the house rocking for what felt like 10-15 secs — Ed Flanagan (@edmundflanagan) August 24, 2014

"Everything was just shaking, the hanging lamps waving back and forth," said Omar Lopez, 24, night clerk at a small inn in St. Helena, 15 minutes outside of Napa. "Guests came into the front desk after the quake and they said the swimming pool looked like a bunch of people had jumped in at the same time."

Three people - two adults and one child - sustained critical wounds. At least 87 people were treated for minor injuries at Napa hospital after the earthquake, the spokesperson told AP. Most patients have cuts, bumps, bruises, said Vanessa DeGier, spokeswoman for the hospital in Napa.

The quake caused six significant fires including a blaze at the Napa Valley mobile home park, where 4 trailers were completely destroyed, according to local firefighters. Up to 16 buildings are now considered uninhabitable; access to many others is restricted.

California Gov. Jerry Brown has declared a state of emergency in Napa. He said conditions of "extreme peril" to people and property exist in Napa, Solano and Sonoma counties.

"There's collapses, fires," said Napa Fire Capt. Doug Bridewel. "That's the worst shaking I've ever been in."

Lots of merchandise damage at the Safeway in American Canyon, CA - pic.twitter.com/v63zE7qXSb — Matthew Keys (@MatthewKeysLive) August 24, 2014

The city government said there were 50 gas main breaks and 30 water main leaks. Three historic buildings in Napa were also damaged, including the county courthouse, and at least two downtown commercial buildings were severely damaged.

"Oh, I felt it. When I woke up I was lying on the floor. It kicked me out of bed," said Keith, a man who lives in Napa adding that he went right into his job at the front desk of a Napa hotel, leaving his house in disorder. "The house is a mess, everything is out of the cabinets in the kitchen. Dressers tipped over."

4 homes total loss, 6-8 damaged. Worst hit accd to Napa fire cpt. #napa#quakepic.twitter.com/cBycmL1xbr — Derek Moore (@deadlinederek) August 24, 2014

At least 15,000 customers were left without power across Northern California, the utility provider Pacific Gas and Electric Company’s map showed following the massive quake.

A look at @PGE4Me's current outage map. Report of 25k without power in Napa, 6k without power in Santa Rosa. pic.twitter.com/7waVUhDcSe — SFGate.com (@SFGate) August 24, 2014

The shaking set off car alarms and had local residents running out of their houses in the middle of the night.

Woke up to our apartment shaking back and forth! Scariest moment of my life! #earthquake#sf — Julia Engel (@GalMeetsGlam) August 24, 2014

The moment the quake struck was captured by CCTV at one of the households in the area - the video is now circulating online.

The USGS initially measured the tremor as “moderate,” but then it was upgraded to "violent." The immediate hours after the event saw at least five aftershocks measuring at 1.6 magnitude. Aftershocks of up to 5.0 magnitude may continue throughout the next week.

Total blackout in Sonoma Valley. None of the traffic lights are working — Peter Fimrite (@pfimrite) August 24, 2014

The quake has been described as the most powerful in the area since the deadly 1989 Loma Prieta 6.9 magnitude earthquake, in which 63 people were killed and more than 3,000 injured.