A magnitude 6.4 earthquake shook the northern California coast early Tuesday morning. 

Preliminary information showed that the 2:34 a.m. PT tremor was centered about 7.5 miles southwest of Ferndale, roughly 300 miles away from San Francisco, according to the U.S. Geological Survey

Videos showed items toppled over in dark homes and some reported hearing their Shake Alert on their phones.

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The Humboldt County Sheriff's Office – the county where Ferndale is located – tweeted that no tsunami was expected, and the power was "out across the county." 

Tracker PowerOutage.US showed 55,376 customers without power. 

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Residents were instructed not to call 911 unless experiencing an "immediate emergency." 

State Sen. Mike McGuire, who represents the county, tweeted that safety evaluations would be taking place following the earthquake and that "aftershocks continue." 

"Humboldt Earthquake: PG&E will begin safety evaluations of both their gas and electrical systems. Power is out to [approx.] 50,000 Humboldt customers. PG&E is currently mobilizing crews to conduct assessments and respond to infrastructure needs," he said.