The strongest earthquake in a quarter century to hit the San Francisco Bay area struck the heart of California's wine country, igniting gas-fed fires, damaging famous wineries and sending dozens of people to hospitals.
The magnitude-6.0 quake that hit early Sunday centred near the city of Napa, an oasis of Victorian-era buildings nestled in the vineyard-studded hills of northern California. The quake ruptured water mains and gas lines, hampering firefighters' efforts to extinguish the blazes that broke out after the temblor struck at 3:20 a.m.
Dazed residents who had run out of their homes in the dark and were too fearful of aftershocks to go back to bed wandered through Napa's historic downtown, where boulder-sized chunks of rubble and broken glass littered the streets. Dozens of homes and buildings across the Napa Valley were left unsafe to occupy, including an old county courthouse, where a 10-foot (3-meter) wide hole opened a view of the offices inside.
Gov. Jerry Brown declared a state of emergency for southern Napa County, directing state agencies to respond with equipment and personnel. President Barack Obama was briefed on the earthquake, the White House said, and federal officials were in touch with state and local emergency responders.
The temblor struck about six miles (10 kilometres) south of Napa and lasted 10 to 20 seconds, according to the United States Geological Survey. It was the largest to shake the San Francisco Bay Area since the magnitude-6.9 Loma Prieta quake struck in 1989, collapsing part of the Bay Bridge roadway and killing more than 60 people, most when an Oakland freeway collapsed.
Queen of the Valley Medical Center in Napa, where an outdoor triage tent was set up to handle the influx, reported treating 172 people in the emergency room, although hospital officials could not say how many of them were there for bruises and cuts suffered in the quake and how many for more routine injuries and illnesses.
Twelve people were admitted for broken bones, heart attacks and other problems directly related to the earthquake, including an adult who remained in critical condition on Sunday night and a 13-year-old boy.
The teen was hit by flying debris from a collapsed fireplace and had to be airlifted to the children's hospital at the University of California Davis hospital for a neurological evaluation. He condition was listed as serious, hospital spokeswoman Phyllis Brown said.
Napa Fire Department Operations Chief John Callanan said the city had exhausted its own resources trying to extinguish at least six fires after 60 water mains ruptured, as well as transporting injured residents, searching homes and collapsed carports for anyone trapped and responding to 100 reports of leaking gas.
Two of the fires happened at mobile home parks, including the one where four homes were destroyed and two others damaged, Callanan said. A ruptured water main there delayed efforts to fight the blaze until pumper trucks could be brought in, he said.
U.S. Rep. Mike Thompson, who represents Napa, said federal and state officials had conducted an aerial survey of the area, but they wouldn't have a cost estimate for the damage until they can get on the ground and into buildings. He said while Napa suffered the worst of it, there also was significant damage about 17 miles south on Mare Island in Vallejo, a former naval shipyard where a museum and historic homes were declared uninhabitable.
Sunday's quake was felt widely throughout the region, with people reporting its effects more than 200 miles (322 kilometres) south of Napa and as far east as the Nevada border. Amtrak suspended service through the Bay area so tracks could be inspected.
Vintner Richard Ward of Saintsbury Winery south of Napa watched Sunday afternoon as workers righted toppled barrels and rescued a 500-pound (227-kilogram) grape de-stemmer that the quake had thrown to the ground.
Mark Ghilarducci, director of the California Governor's Office of Emergency Services, told an afternoon news conference some 90 to 100 homes and buildings were deemed not habitable.
Pacific Gas and Electric spokesman J.D. Guidi said some 30,000 customers lost power after the quake hit, but that number was down to around 7,300 later in the day, most of them in Napa. He said crews were working to make repairs, but it was unclear when electricity would be restored.
The depth of the earthquake was just under seven miles, and it was followed by numerous small aftershocks, the USGS said.