U.S. Geological Survey shook a wide swath of the Bay Area awake early Sunday.
Centered about nine miles south of wine country's Napa at 3:20 a.m., the quake was felt as far south as Santa Cruz and into Sonoma County. It was the largest earthquake to strike the Bay Area since the Loma Prieta temblor of 1989, the USGS said.
Residents reported power outages in Napa, and fire departments in several counties, along with the California Highway Patrol, were on the lookout for damage to bridges.
Reports were beginning to stream in of gas leaks, downed power lines and at least one fire.
Napa County Fire Department confirms they are swamped with calls, including reports of injuries. It is unclear how severe the injuries are because units are still responding.
Queen of the Valley Medical Center in Napa reported calls of injuries, mostly cuts from glass.
According to PG&E, more than 42,000 customers are without power across the northern Bay Area, including American Canyon, Napa, Saint Helena, Santa Rosa and Sonoma, according to an outage map.
Pictures flooding in from Twitter show damage within homes.