A strong earthquake has struck the US West Coast, triggering urgent warnings for millions to shelter in place during the seismic shockwaves.

The US Geological Survey said a magnitude 5.6 quake erupted in Northern California at 11.10am ET on Wednesday, marking the strongest tremor since 1940.

While the strongest shaking was reported right at the quake's epicenter near Redwood Valley, the tremors traveled more than 600 miles up and down the West Coast, reaching Coos Bay, Oregon in the north and Salinas, California in the south and parts of western Nevada.

A security camera inside the home of a Kelseyville resident, about 40 miles east of the epicenter, captured the moment his home began to shake that lasted for about 30 minutes. 

The footage shows framed photos falling off the walls and a computer monitor tipping over.  

Power outages are affecting more than 6,000 residents of six towns near the epicenter, the office said in a statement, and encouraged people to stay off the highways and roads to allow work crews to inspect for damage and make repairs. 

Moneca Vargas at Saint Mary's Catholic School in Ukiah told KTVU: 'That was the biggest earthquake I have felt in my life, and I’ve lived in Ukiah for most of my 54 years. My whole house shook.'

Other residents close to the source in Northern California compared the shockwaves to a 'freight train' rolling through their homes, causing items to fall from shelves and officials to sound the official earthquake alert system for quakes stronger than magnitude 4.5.

While the shockwaves reached level seven in certain areas, meaning 'very strong' shaking and moderate damage, according to USGS, there have been no reports of injuries at this time. 

Since the initial quake, over six aftershocks have been recorded in less than two hours, all measuring stronger than magnitude 2.0. 

USGS has warned that there is a nearly 90 percent chance of another earthquake stronger than magnitude 3.0 erupting in the region over the next week.

Experts added there is a 40 percent risk of a quake stronger than magnitude 4.0 and a slim-but-not-impossible seven percent chance of another quake over magnitude 5.0 striking the West Coast this week. 

The epicenter of Wednesday's earthquake was recorded within seven miles of the Maacama Fault zone.

The Maacama is a major active strike-slip fault capable of causing strong shaking and damage in areas like Mendocino and Sonoma counties, where it runs through rural communities and wine country.

Making the fault even more of a concern to locals is the fact that it is part of the larger San Andreas Fault system, the infamous 800-mile-long fault running through much of California.

USGS scientists have documented that the Maacama Fault has produced large earthquakes in the past and could potentially generate one in the future, which could exceed magnitude 7.0.

According to a 2015 report, there is a 95 percent probability that at least one major quake, stronger than magnitude 6.7, will strike somewhere in the Bay Area by 2043.

Just as the California Governor's Office of Emergency Services warned roughly 657,000 people to 'drop, cover and hold on' using the MyShake App, the American Red Cross is explaining how these steps could save your life.

The Red Cross noted that dropping to your hands and knees protects you from being knocked down during the seismic waves and allows you to crawl to a more protected space.

Next, safety experts urge you to cover your head and neck with your arms. 

'If a sturdy table or desk is nearby, crawl underneath it for protection. If you cannot find a protected space, crawl to an interior wall (away from windows),' the Red Cross recommended in a statement. 

Lastly, do your best to hold on until the shaking stops. If you were able to make it to a desk or table, hang on to the table while protecting your head with one arm.