NAPA, Calif. — A magnitude 6.0 earthquake struck the area north of San Francisco early Sunday, injuring about 120 people, causing extensive damage to buildings in downtown Napa and Vallejo, sparking fires and gas line breaks, and cutting power to thousands.
The quake, the largest in the Bay Area since the deadly Loma Prieta earthquake of 1989, struck 3 miles northwest of American Canyon at 3:20 a.m., the US Geological Survey said. It was felt as far away as Chico and Fresno.
Governor Jerry Brown declared a state of emergency for southern Napa County, directing state agencies to send equipment and personnel to affected areas, including Napa, Solano, and Sonoma counties. President Obama was briefed on the quake, and federal officials were in touch with state and local officials.
Hardest-hit was Napa, about 6 miles north of the quake’s epicenter. Officials at Queen of the Valley Medical Center in Napa said three of the 120 injured people were in critical condition, including a boy who was hurt by debris from a chimney. The boy was airlifted from Napa to a trauma center.
Many of the injured suffered concussions, cuts, and bruises, officials said.
About 30,000 homes and businesses lost power in the quake. Late Sunday, about 19,000, mostly in Napa, remained without power. Crews were working to make repairs, but it was unclear when service would be fully restored.
Sixty water mains were broken in Napa, and Pacific Gas and Electric Co. said it had 50 reports of broken gas lines.
There were also problems in Vallejo, where officials said 41 buildings were damaged, including businesses, several homes, and a church.
Scientists said the quake was 6.7 miles deep and may have hit on the West Napa Fault. It was the largest in the Bay Area since the 6.9-magnitude Loma Prieta quake killed 62 people on Oct. 17, 1989.
The West Napa Fault is one of several parallel faults in the earthquake-prone region. The rupture was believed to be in the Browns Valley section of the fault, about 3 miles northwest of American Canyon.
Later on Sunday, a 6.9-magnitude earthquake struck a sparsely populated area of central Peru, the US Geological Survey said. There were no immediate reports of damage or injuries, according to the Associated Press.
In Napa, City Manager Mike Parness said most of the quake damage was confined to a few sections of the city, but officials said it will be weeks until those areas are cleaned up.
Officials at Queen of the Valley Medical Center set up a triage tent in the parking lot. In the first hours after the quake, ambulances were arriving every few minutes dropping off patients.
John Callanan, operations chief for the Napa Fire Department, said the department used all its resources to extinguish at least six fires after the 60 water mains ruptured. It also transported injured residents, searched homes for anyone trapped, and responded to reports of gas leaks.
One of the worst scenes of damage was at the Napa Valley Mobile Home Park, where a fire burned at least four homes. A broken water main there hampered firefighters’ efforts to control the blaze. Water trucks were brought to the scene. There were no injuries.
The cause of that fire was unknown, and PG&E said its natural gas lines were not responsible.
In downtown Napa, bricks, concrete chunks, and broken glass littered the streets. About 15 buildings were red-tagged, meaning the structures were uninhabitable and public access was barred.
Numerous other buildings were yellow-tagged and allowed to open on a limited basis, officials said.
Napa’s Old County Courthouse and the post office were among the buildings that sustained damage. Emergency workers usually stationed there were moved to the sheriff’s office.
Most of the windows were blown out of the air traffic control tower at the Napa County Airport. The structure will be unusable for several weeks, said Ian Gregor, a spokesman for the Federal Aviation Administration.
Across Napa, dozens of unreinforced chimneys toppled, tilted, or leaned precariously from houses. “It was just like a train hit the house,’’ Cathy Hunt said as she surveyed a pile of bricks that used to make up the chimney of her home on Montgomery Street.
At Napa Barrel Care, a wine warehouse just south of the city, Carole Meredith surveyed an array of tumbled barrels.
‘‘We’re physically fine but we’re emotionally shell-shocked,’’ Meredith said. Although it is too soon to know the extent of loss, she said, ‘‘there is a lake of wine on the floor.’’
Because wines from the bountiful 2013 vintage are mostly still in barrels, ‘‘there’s just going to be huge losses,’’ said Meredith, who owns the Lagier Meredith winery on Mount Veeder. ‘‘This is going to be a really expensive earthquake for the wine business.’’
Napa’s two water treatment plants were undamaged, although water-main breaks knocked out service to some areas. The water that is available is safe to drink, officials said.
California transportation officials checked the Bay Area’s toll bridges after the quake and found them to be safe. On Highway 121 in the North Bay, 30 feet of asphalt was cracked, but the road was open.
Napa residents and city officials said the toll would have been far greater had the quake struck on Saturday, when thousands of people were downtown enjoying the Napa Blues, Brews, and BBQ event.