The earthquake occurred at about 2:34 a.m. near Ferndale, a small community in Humboldt County. It was followed by at least 80 aftershocks.
At least 12 individuals have been injured, with none critically, officials said. Two individuals, ages 72 and 83, have died as a result of medical emergencies occurring during and/or just following the earthquake, according to Humboldt County Sheriff William Honsal.
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Those injuries include at least one broken hip and a head injury.
"We aren't tracking all of the injuries that are coming in now because they are coming in quite quickly now... but as far as we know there is nothing critical," said Sheriff Honsal.
According to a PG&E spokesperson, as of 4 a.m. on Wednesday, power has been restored to over 55,000 customers in Humboldt County. This leaves less than 15,000 customers without power. At the height of the outages, 71% of customers in the county were without power.
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In a Tuesday afternoon update, officials said the water system is still not working in Rio Dell. They don't expect it to be back on Tuesday night. The town could be 24-48 hours without running water, according to ABC7's Liz Kreutz. A boil water advisory has been issued for Rio Dell and Fortuna.
Officials say Rio Dell is "ground zero" for damage from the earthquake.
So far, 15 homes in Rio Dell have been red-tagged which means they are not safe for occupancy. At least 18 homes have been yellow-tagged. Officials say they have checked roughly 50% of the homes.
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Humboldt County Sheriff PIO Samantha Karges confirms there were rescues Tuesday morning, saying, "Yes, two structure collapses with entrapment."
She says she can't say at this time if those are the same as the two people injured or if the two people rescued were injured.
VIDEO: At least 80 aftershocks reported after 6.4 Humboldt Co. earthquake, CAL OES says in 11 a.m. press conference
At least 80 aftershocks reported after 6.4 Humboldt Co. earthquake, CAL OES says
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Emergency officials say "widespread damages" have been reported to roads and homes throughout Humboldt County. PG&E says it has initiated its emergency response plan and crews are responding to gas and electric hazards.
Humboldt County District 2 supervisor Michelle Bushnell tells ABC7 News it's a "total mess" in the city, with houses off their foundation and no power or water into the city after a major water main break.
Residents in the area have been posting video showing the damage to their homes. There are reports of gas leaks in the area and at least one bridge has a large crack through it.
Out of an abundance of caution, Fernbridge -- connecting Ferndale -- will be closed for further inspection, according to Sen. Mike McGuire. CalTrans will remain on scene to assess the structure.
The quake triggered a massive response by the MyShake App that detects the start of a quake and sends alerts to cellphones in the affected region that can give people notice to take safety precautions in the seconds before strong shaking reaches them.
The system pushed out alerts to some 3 million people in Northern California early Tuesday, Ghilarducci said. "The system did operate as we had hoped," he said.
This earthquake did not trigger a tsunami warning.
Governor Gavin Newsom proclaimed a state of emergency for Humboldt County to support the emergency response to the earthquake. The emergency proclamation enables Humboldt County to access resources under the California Disaster Assistance Act, including directing Caltrans for immediate assistance and supporting impacted residents by easing access to unemployment benefits and waiving fees to replace public records.
Newsom issued a statement on Tuesday writing:
"Jennifer and I send our heartfelt condolences to the families grieving the loss of loved ones and offer our best wishes for the recovery of those who were injured in this earthquake," said Governor Newsom. "California stands with the people of Humboldt County and the state has moved quickly to support the emergency response underway with local and tribal partners. I thank all of the women and men who have mobilized to protect public safety and support the community at this challenging time."
Gov. Newsom's office activated the State Operations Center to coordinate the ongoing emergency response with local and tribal governments and provide any needed resources, including shelter, food and water, and aid in damage assessments of buildings and roadways.
The Red Cross said in a tweet it opened an emergency shelter located at:
Fortuna Fireman's Pavilion
9 Park Way, Fortuna, CA 95540
The earthquake came just days after a small magnitude 3.6 earthquake struck the San Francisco Bay Area, waking up thousands of people before 4 a.m. Saturday and causing minor damage.
That earthquake was centered in El Cerrito, about a 16-mile drive to downtown San Francisco.
Stay with ABC7 News for updates on this developing story.
The Associated Press contributed to this report.
Click here for the latest stories and videos about earthquakes here in the Bay Area and around the world, and click here for more information on disaster preparedness.
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