(CNN) -

The strongest earthquake in 25 years in Northern California struck early Sunday, injuring dozens of people, damaging historic buildings in downtown Napa and turning fireplaces into rubble.

The 6.0-magnitude quake struck just six miles southwest of Napa, California's famed wine country.

"Everything and everyone in Napa was affected by the quake. My house, along with everybody else's, is a disaster. It looks like somebody broke in and ravaged the place, room by room," said CNN iReporter Malissa Koven, who was awakened by the shaking at about 3:20 a.m.

"Anything and everything that could fall, did," she said.

One child was hurt when a fireplace collapsed and was airlifted to UC Davis Medical Center, hospital spokeswoman Vanessa deGier told CNN.

Nearly 160 were treated for minor injuries at the emergency room at Queen of the Valley Hospital, though hospital CEO Walt Mickens could not confirm that all of those patients were injured in the earthquake.

Thirteen people were admitted for orthopedic issues and medical conditions, according to Mickens. The remainder were treated and released, suffering from bruises and lacerations, he said. By Sunday night, only one patient was still in critical condition.

Assessing the aftermath

The damage in Napa is "fairly significant," said Glenn Pomeroy, the CEO of the California Earthquake Authority, who surveyed the area Sunday afternoon.

At least 15,000 customers in and around Sonoma, Napa and Santa Rosa lost power, according to Pacific Gas and Electric Company. Roughly 7,300 were still without power as of Sunday evening.

In historic downtown Napa, the bricks and beams that once made up buildings' facades lay splayed in the street. Shattered glassware covered the floor of a local restaurant. One home had visible charring from a fire that occurred in the aftermath of the quake. Gas leaks and downed power lines were also reported.

"The post office building had cracked, the local hardware store was destroyed with layers of shelves that had fallen over and busted the windows, multiple buildings had fallen apart, and all the local businesses looked trashed on the inside and out," Koven said.

Pomeroy said that downtown was particularly hard hit "probably because of the age of construction."

However, the damage "is not as bad as it could have been," Mark Ghilarducci, the director of the California Office of Emergency Services, said at a news conference Sunday.

Putting out the fires

To help with the recovery Gov. Jerry Brown declared a state of emergency.

"We're here for the long run," Lt. Gov. Gavin Newsom told CNN. "Not just when we're putting out fires -- literally."

The earthquake triggered six major fires that destroyed several mobile homes, said Napa Division Fire Chief John Callanan.

Napa Public Works Director Jack Rochelle said it might take up to a week to get the water system back to normal after dozens of water main breaks were reported. The water that is still flowing is safe to drink, he said.

How did it feel?

Sunday's earthquake struck four miles northwest of American Canyon, six miles southwest of Napa and nine miles southeast of Sonoma, according to the USGS.

The USGS estimated that based on their locations, 15,000 people experienced severe shaking, 106,000 people felt very strong shaking, 176,000 felt strong shaking and 738,000 felt moderate shaking.

For those in Napa, close to the epicenter, the quake jolted downtown residents such as Karen Lynch.

"It was not like other quakes we have felt," Lynch told CNN. "This was a violent quake."

Although the quake has not resulted in any deaths so far, many residents were surprised by how strong it was.