CALIFORNIA has been struck by a swarm of 28 earthquakes in just 24 hours as fears of a “big one” cause alarm across the US state.

The US cities of Los Angeles, San Francisco and Sacramento have all been rattled by large earthquakes 1.5 magnitude or greater in the past day.

The largest quake measured 2.6 magnitude and struck 4.30am local time at a depth of 23km near Tuolumne City, around 213km from San Francisco.

Eleven of the tremors were over 2.0 magnitude, while the rest were between 1.0 to 2.0 magnitude, according to Earthquake Track.

Although relatively small, the wave of earthquakes will entrench fears that a massive tremor measuring 7.0 or above could strike the region.

Scientists believe the US state is overdue a “big one” magnitude 7 or over earthquake by around 50 years.

Last week a magnitude 3.6 earthquake rattled northwest Los Angeles after striking in the Santa Monica mountains.

It struck in the same week a colossal 7.1 magnitude virtually flattened Mexico City, causing widespread damage and killing more than 300.

Over the weekend Mexico was shaken by more quakes, including a 6.2 tremor that caused people to flee their homes.

Since then experts have issued warnings that a powerful earthquake akin to the one that hit Mexico is “inevitable”.

“The system that is causing these quakes in Mexico is by and large similar to what’s happening in California.”

Natural disaster expert Matthew Blackett, of Coventry University, said the system causing the Mexico earthquakes is similar to the one in California.

“It’s a different system,” he said. “But the system that is causing these quakes in Mexico is by and large similar to what’s happening in California.”

Colliding tectonic plates are causing the earthquakes on both continents, which sit in a tremor disaster zone known as the Ring of Fire.

An 800-mile fissure that runs almost the length of California is thought to be the cause for most concern.

Over the past 150 years, pressure has been building up along the San Andreas fault that experts believe could unleash the next “big one”.