A powerful earthquake has hit the coast of north California - and there are warnings of more to come.
The magnitude 6.9 quake struck late on Sunday night (5.18am UK time) beneath the Pacific seabed.
The epicentre was 48 miles west-northwest of the town of Ferndale at a depth of 4.3 miles.
Although there were no reports of injuries or damage, the quake was felt in San Francisco, which lies 250 miles from Ferndale.
Worryingly for Californians, the US Geological Survey (USGS) is warning of a 90% probability of a "strong and possibly damaging aftershock" of magnitude 5 or more in the next seven days.
There is a 5-10% chance of a quake equal to or greater than Sunday's tremor, which prompted more than 3,000 reports to the USGS website.
"This lasted longer than any earthquake I've ever felt," Ferndale resident Raquel Maytorena told The Los Angeles Times.
"It just kept going and going, very slowly and softly. It was not violent. It almost felt like you were in a boat that was rocking."
Mrs Maytorena said she felt the quake for 20 seconds.
Up to 300 small aftershocks can be expected over the next week but for now there is no tsunami danger, experts said.
Californians have long been braced for a potentially devastating earthquake.
The state is on the so-called Ring of Fire, which has produced numerous destructive quakes including Japan's March 2011 quake-tsunami, which killed thousands.
Geologists predict a quake capable of causing widespread destruction to California is 99% certain in the next 30 years.
A 6.7 magnitude earthquake in Los Angeles killed at least 60 people and caused $10bn (£5.8bn) damage in 1994.
A 6.9 quake in San Francisco in 1989 left 67 people dead.
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