San Francisco Bay Area residents have been shaken out of their slumber by a magnitude 4.4 earthquake that was felt over a wide area.

The quake struck at 2.39am about 2 miles (3km) from Berkeley, just across the bay from San Francisco, according to the US Geological Survey.

The magnitude was revised after it was initially reported as magnitude 4.5. It happened at a depth of 8 miles (13km).

The quake struck about 2 miles (3km) from Berkeley, just across the bay from San Francisco (USGS)

Social media posts showed people were woken up some 40 miles (64km) to the north and south.

A spokesman for the California Governor's Office of Emergency Services said there were no reports of harm to the region.

A Berkeley Fire Department dispatcher, who declined to give his name, said more than a dozen people had called, mostly complaining about windows shaking. He also said there were no reports of any damage or injuries.

“Felt like a big truck drove into the building or something blew up downstairs. It just rocked the room and bed like two or three times quickly with a decently loud rumble in North Berkeley,” Dale Fest wrote on the San Francisco Chronicle's Facebook page .

Bay Area Rapid Transit said it had checked tracks for damage and found no problems. Early delays in train service were cleared up by 5.30am, the agency said.

Jack Boatwright, a geophysicist with the USGS Earthquake Science Center in Menlo Park, said the shaking from the quake “seemed a little weak, about half as strong as what you would expect.”

He told the Chronicle that by 4.15am, there had been no aftershocks, which he called “a good sign. It may mean less likelihood of a larger earthquake to follow.”

Twitter lit up with comments, many of them light-hearted.

"Since everyone in the Bay Area is awake, it's time for the 30 minute dance party! #earthquake," one user wrote.

Another described how the earthquake woke them up: "*wakes up to earthquake in san francisco*, *freaks out*, *checks twitter*, *goes back to bed*"

Around an hour after the quake, San Francisco's Department of Emergency Management sent a text to residents saying there was no tsunami warning.