The "terrifying" 4.5 magnitude quake struck the huge US city of San Francisco shortly before 3am local time (10am UK).
The "strong" tremor woke thousands of people up with many taking to social media fearing it was the dreaded "Big One".
One tweeted: "Wow! Just experienced a major earthquake in San Jose, California. Brace for after shocks..."
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Another wrote: "Omg, the earthquake scared me! So unexpected and different from others."
And one said: "There was an earthquake just now and i was fully expecting it to be the big one that destroys California".
The quake's epicentre struck Berkeley, which is a city on the east shore of San Francisco Bay.
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It is the biggest to strike California in three years.
The quake will now spark fresh fears "The Big One" – an "inevitable" magnitude 7.0 earthquake or greater – is imminent.
In 2008, the US Geological Survey found there was a 99% chance of a huge quake hitting California, which sits on the San Andreas fault which is part of the "Ring of Fire".
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This is a long belt that runs along the Pacific Ocean where a large number of earthquakes and volcanic eruptions occur.
A report warned how a huge quake of this size could kill 1,800 people, injure 53,000, and cause $214billion (£162billion) of damage.