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Millions of people across southern California have been taking part in what organisers say is the biggest-ever US earthquake drill.

Schools, hospitals and businesses joined in the exercise known as "The Great Southern California Shake-out".

The drill was based on the hypothetical scenario of a magnitude 7.8 earthquake striking the southern portion of the San Andreas Fault.

It was devised by scientists to help people prepare for future earthquakes.

At precisely 1000 local time (1800GMT), when the earthquake is supposed to have struck, millions of participants followed instructions to "drop, cover and hold on" - drop to the ground, take cover under a sturdy desk and hold on until the shaking stopped.

They were guided by a public service message sent to buildings and broadcast by television and radio stations.

Search and rescue

At the University of Southern California in Los Angeles, a sports field was set up as a triage centre, with "injured" victims, some wearing gory make-up, being ferried to hastily erected hospital tents.

At the California Institute of Technology (Caltech) in Pasadena, search and rescue teams were deployed to find victims trapped in a maze of cardboard boxes simulating survivors buried in rubble.

Fire crews, police and medical emergency services also took part in exercises at several locations.

"If you are prepared, it gives you an automatic sense of calmness because you have the tools and equipment necessary to function," Los Angeles Fire Department Captain Steve Ruda told reporters.

Organisers say 300 scientists have worked together on the scenario for the drill

The imagined earthquake would, they say, cause 2,000 deaths, 50,000 injuries and $200bn (£134bn) in damage.

California is one of America's most earthquake-prone states.

The US Geological Survey says it faces a 46% chance of being hit by a magnitude 7.5 or higher earthquake in the next 30 years.

The last major earthquake to strike California was in 1994, when a magnitude 6.7 strike left 57 people dead.

The great San Francisco earthquake of 1906 was about 7.8 and caused some 3,000 deaths in collapsed buildings and fires.