A light earthquake has shaken California's San Francisco Bay Area, waking many, but there were no immediate reports of damage.
The US Geological Survey (USGS) said the shallow quake was of magnitude 4.5 and occurred at 2.39am (local time) on Thursday. Its epicentre was in Berkeley, across the bay from San Francisco.
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.
The USGS placed the epicentre of the earthquake next to the Claremont Club and Spa in Berkeley. The historic luxury hotel had no damage, an employee said, declining to give her name.
"Since everyone in the Bay Area is awake, it's time for the 30 minute dance party! #earthquake," a Twitter user with the name @Troop206Oakland wrote in a message, as the social media service lit up with comments, many light-hearted.
About an hour after the quake, San Francisco's Department of Emergency Management sent a text to residents saying there was no tsunami warning.