More than 70,000 without power after 6.4-magnitude earthquake rattles Northern California

A 6.4-magnitude earthquake rocked coastal Northern California early Tuesday, leaving thousands in the dark as officials warned that another major jolt could still be on its way.

The quake hit at a depth of 10 miles just after 2:30 a.m. PT near Eureka in Humboldt County, the U.S. Geological Survey said. It struck around 7.4 miles west-southwest of Ferndale, the agency said.

As many as 80 aftershocks followed, with the most powerful being a 4.6-magnitude jolt that rocked the city of Rio Dell, according to Mark Ghilarducci, director of California's Office of Emergency Services.

At least two people were injured, the Humboldt County Sheriff's Office said. One person's hip broke and another sustained a head injury, it said.

Speaking about nine hours after the initial earthquake, Ghilarducci said there were no known fatalities.

"We live in earthquake country and this another example of the fact that earthquakes can happen at anytime without  notice," Ghilarducci told reporters at the office's headquarters in Mather.

"And so it’s really important that we, as Californians, have a plan, have a family plan, have some supplies in case we lose power."

State officials urged Humboldt County residents to be prepared for another quake.

There’s a 13% chance of another powerful jolt, of a 5.0-magnitude or stronger, striking in the next week, according to Cynthia Pridmore, a senior engineering geologist with the California Geological Survey.

She told Humboldt County residents to gather food, water, flashlights and other supplies.

“People do need to be prepared, especially if they’re in weakened structures to be mindful of where they’re staying,” she said.

More than 68,000 homes and businesses throughout Humboldt County were still without power by 11:40 a.m. PT, Pacific Gas and Electric reported.

The city of Eureka set up a charging station for residents without power to plug in their phones, computers and medical equipment while police urged shopkeepers to keep an eye on their storefront as there "have already been several reports of burglaries to businesses."

"Power is out across the county," Humboldt County's Office of Emergency Services said in a tweet, adding: "DO NOT CALL 911 UNLESS YOU ARE EXPERIENCING AN IMMEDIATE EMERGENCY."

The county sheriff's office said widespread damage to roads and homes had been reported across the county as it warned residents to "be prepared for aftershocks" and to check gas and water lines for damage or leaks.

"Exercise caution if traveling," it added.

A section of the historic Fernbridge in Ferndale was closed due to "possible seismic damage," the California Department of Transportation said. In a photo it shared online, cracks could be seen on the bridge.

Mike Shapiro, a car salesman from Eureka, said Tuesday's quake jarred him awake before knocking him down.

"I got up, took two steps and ended up on the floor. The second jolt just took my feet out from under me," Shapiro, 54, told NBC News. "I"m fine, just spent three hours picking up broken glass."

Shapiro vividly recalled the 1992 Cape Mendocino earthquakes and said he's dutifully strapped down furniture and appliances ever since.

"Earthquakes generally don't make me nervous, but this one made me nervous," Shapiro said. "I'm just glad everything was strapped down, nothing fell on us."

There was no threat of a tsunami in connection with the earthquake as of early Tuesday, the National Weather Service's tsunami warning system said.

A number of people said on social media that they were woken up by the MyShake earthquake warning app on their cellphones.

A seismologist with the USGS said people living near the coast reported feeling "significant shaking." They said people could expect to see minor damage, including things falling off shelves, and could possibly see foundational damages.

The quake comes almost exactly a year after a 6.2-magnitude earthquake struck offshore in the Cape Mendocino area of Northern California on Dec. 21 last year. No major damage or injures were reported in connection with that quake.

That earthquake had struck at a depth of 5.6 miles in the Pacific Ocean, about 24 miles west of the small community of Petrolia along the rocky wilderness of California’s Lost Coast region in Humboldt County, the Geological Survey and the Humboldt County Sheriff’s Department said at the time.

Cal Poly Humboldt was already on winter break but the school asked everyone, but essential personnel, to stay off campus as inspectors assess damage.