An earthquake of magnitude 4.6 in Northern California awakened residents with a jolt early Thursday, with many saying they felt their homes shake for a few seconds in a 161-kilometre stretch, including San Francisco.
The earthquake was centred 1.6 kilometres from Boulder Creek in the Santa Cruz Mountains, the US Geological Survey reported.
It happened at about 1:40 am.
There were no immediate reports of serious damage.
Boulder Creek, which has about 5,000 people, is about 105 kilometres southeast of San Francisco. Residents as far north as Petaluma, about 64 kilometres north of San Francisco, also said they felt it.
Some residents said they were first awakened by earthquake alerts on their phone, then felt their beds and windows shake.
In February, a series of small earthquakes rattled the San Francisco Bay Area. The most powerful quake was a magnitude 4.2 that struck south of San Ramon, according to the USGS.
At least a dozen other smaller quakes struck in the same area.
The area east of San Francisco has experienced earthquake swarms - when multiple small magnitude earthquakes strike over a short period of time - for decades, according to seismology experts.