LOS ANGELES - MILLIONS of people across California took part in the biggest earthquake drill in US history on Thursday, a large-scale exercise aimed at testing the region's readiness for a seismic disaster.

Thousands of schoolchildren, students and workers were among an estimated 5.2 million Southern Californians who took cover under tables and shelters just after 10.00am (2.00am Singapore time) as a mock 7.8-magnitude earthquake hit the region.

Firecrews, police and medical emergency services were taking part in exercises at multiple locations throughout the morning.

Dubbed the 'Great Southern California Shakeout', the exercise simulates a large earthquake on the San Andreas Fault that leaves 1,800 people dead, 53,000 injured and 1,500 buildings destroyed.

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 a football field next to a hospital in the suburb of Mission Hills, around 300 students from nearby Bishop Alemany High School high school were being treated for mock injuries including broken legs and severed arteries.

'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 at the scene.

Sean Parker, a 17-year-old student, was portraying a casualty clutching a head injury caused by a falling classroom fan. 'You live in California, there's going to be an earthquake,' he said. 'There always is.'

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

Even local broadcasters got into the spirit of the occasion, with Fox 11 News covering mock news briefings featuring seismologists gravely informing reporters of the epic nature of the disaster.

According to the USGS, a 7.8-magnitude shake would rattle buildings in Los Angeles for 55 seconds, compared to the seven seconds it shook during the 1994 Northridge quake, which left 72 people dead and 12,000 injured.

Geologists say an earthquake capable of causing widespread destruction is 99 per cent certain of hitting California within the next 30 years.

California Governor Arnold Schwarzenegger said on Thursday he had alerted state emergency officials to swing into action at 5.00am local time - five hours before the official start of the drill - to test their readiness.

'I was really impressed and amazed about the quick response - how quickly I was picked up at my home, how quickly we had the satellite phones ready and hooked up in order to be ready to communicate,' Mr Schwarzenegger said.

'I have to say to the people of California, they can be proud of the quick response. We do have the best responders in the world. We've seen it in the fires, you know, every single year.'

US Geological Survey seismologist Lucy Jones said the drill would serve to highlight the importance of preparedness from the bottom up, emphasising that homeowners should start by ensuring buildings had been properly reinforced.

'If I've made my house safer and my neighbour hasn't, we're all in this together, we each have a role to play,' Ms Jones said on Wednesday. 'That's the message that we're trying to get through.

'Southern California is more ready than any other place in the US. But there is a lot more that can be done.' -- AFP