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California has been struck by a series of rapid earthquakes erupting right along what experts call 'America's most dangerous' fault line.

The first earthquake struck right in the heart of California's Bay Area at 11.30am ET (8.30am local).

The US Geological Survey (USGS) initially measured it as a magnitude 4.1 earthquake just 14 miles from San Francisco. That measurement was quickly downgraded to a magnitude 3.8 tremor.

That quake was followed by three more tremors less than an hour later, striking in rapid succession between 12.07 and 12.38pm ET.

Those aftershocks were measured at magnitude 3.0, 2.8 and 1.7, respectively.

The San Francisco-Bay Area is home to nearly eight million people. Thousands of people reported feeling the initial earthquake, with some reports coming in from as far away as Sacramento, roughly 75 miles east of San Francisco.

The earthquake swarm took place right along one of California's most concerning seismic regions - the Hayward Fault.

The Hayward is a 74-mile-long fault line that is part of the massive San Andreas fault system. Like the more famous San Andreas, the Hayward is capable of producing a devastating earthquake stronger than 7.0 in magnitude and is considered extremely overdue for a major seismic event.

Four minor earthquakes have struck the California Bay Area on August 13

USGS scientists have previously warned that an earthquake stronger than magnitude 6.7 has a 95 percent chance of striking near the Bay Area (Pictured) by 2043

Thursday's earthquakes produced relatively light shaking throughout the Bay Area, according to USGS.

However, Bay Area Rapid Transit (BART) train service in the area was stopped during the event and is now running with delays of up to 20 minutes throughout the rail system. No injuries have been reported.

The last time a major earthquake erupted along the Hayward was 158 years ago in 1868, but scientists have calculated that this fault typically ruptures every 95 to 183 years.

A team from California's Lawrence Livermore National Laboratory said in a statement: 'The fault is overdue for an earthquake that could cause extensive damage to such a dense population zone.'

An analysis by the University of California, Berkeley determined the Hayward fault has a 33 percent chance of rupturing and producing a major magnitude 6.7 earthquake or greater by 2043.

Researchers at USGS have previously warned that there was a 72 percent chance of such a disaster striking the Bay Area in the next two decades, along the Hayward or another major fault in the area.

This is a breaking story. More details to follow.

The first, a magnitude 3.8 quake, was reported by thousands of residents from Sacramento to San Francisco