(Updates with reports of some damage, USGS comment, resident comment)
SAN FRANCISCO, Aug 24 (Reuters) - An earthquake of 6.0 magnitude, the largest in the region for 25 years, shook the San Francisco Bay Area early on Sunday, waking residents and causing some power outages and minor damage, according to initial reports.
The U.S. Geological Survey (USGS) said the epicenter of the quake was eight km (five miles) northwest of the town of American Canyon, on the northern edge of the Bay.
Randy Baldwin, a USGS geophysicist, said the tremor was potentially damaging because it was close to populated areas.
He added the USGS was starting to receive reports of some damage in the city of Napa, mostly masonry and some structural damage, as well as power outages.
Local CBS news said that several fires had broken out in Napa, which is famous as a wine-growing center.
A safety dispatcher for several cities, including American Canyon and Napa, said there were reports of people losing power.
Police dispatchers in nearby San Francisco and Oakland said there were no reports of major damage.
"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 and who wanted to be identified only by his first name.
He said 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."
The quake was the largest to hit the Bay area since the Loma Prieto quake in 1989.
"It is the strongest quake in a 60-mile (100-km) radius from the epicenter of this quake in several decades," Baldwin said.
Reuters reporters in Oakland felt the quake as a long, low swell that shook gently for several seconds.
"It was a shallow quake and there are lots of aftershocks," Baldwin said, adding most were around magnitude 2 range.
Aftershocks can continue for the next several weeks and experts will watch their distribution to determine if this quake happened on a fault line, he said. (Reporting by Andrew Roche, Dan Levine, Peter Henderson and Fiona Ortiz; Writing by Peter Henderson and Dina Kyriakidou; Editing by Frances Kerry)