Los Angeles - Over 5 million Californians ducked for cover and held Thursday as they took part in what was billed as the largest public emergency drill in US history.

Some 5,000 first responders and emergency managers were also involved in The Great ShakeOut drill, which was designed to simulate the effects of a 7.8 magnitude quake on the San Andreas Fault across the densely populated area of Southern California.

If it actually occurred, a quake of this strength could kill about 1,800 people and injure 53,000. Damages would reach an estimated 213 billion dollars.

The drill began at 10 am Thursday throughout the greater Los Angeles and San Diego urban areas and beyond, where radio and television stations and school public address systems played a sound track of rumbling and crashing, along with a man's voice.

"If this were the magnitude 7.8 earthquake we're practicing for today, you would be experiencing sudden and intense back-and-forth motions of up to 6 feet (2 metres) per second. The floor or the ground would jerk sideways out from under you. Look around and imagine," the voice said.

The drill - in which people were supposed to dive under their desks, cover their heads and hold on - was to be followed by a "Get Ready Rally" in which people would learn about other aspects of quake preparedness. There was also a three-day conference of earthquake experts planned and even two computer games - one called After Shock, and another called Beat the Quake.

Some 3 million students in Los Angeles and Riverside county schools are among the 5.2 million participants in the drill.

According to research published in April there is a 99.7 per cent chance that a magnitude 6.7 or stronger quake will shake California within the next 30 years. The southern end of the San Andreas fault hasn't moved in 300 years, yet historically it moves on average every 150 years. (dpa)