Monday's temblor, measuring 6.5 on the Richter scale, also injured 40 people, completely demolished a historic building in the town of Paso Robles, damaged scores of others and cut power to thousands of residents.

The most deadly quake to hit the region since a 7.1 hit Los Angeles in 1994 killing 57 people and causing billions of dollars of damage, served as a stark reminder of the biggest threat to California.

"This was certainly a shocking reminder to people who live just about anywhere in California that we are prone to earthquakes and should do what we can to prepare," Caltech seismologist Thomas Heaton told AFP.

High-rise buildings from Los Angeles to San Francisco -- almost 400 kilometers (240 miles) from the epicenter -- swayed wildly as the temblor roared through the central coastal region of the most populous US state.

As California's Governor Arnold Schwarzenegger prepared to visit the stricken region Tuesday, strong aftershocks shook the area that lies halfway between Los Angeles and San Francisco.

A wave of shocks measuring between three and 4.2 on the Richter Scale jolted the area through the night, keeping nervous residents awake and prepared to flee another quake.

"About one in 20 earthquakes are followed by a bigger one within a week or so, but the fact that it did not happen in the first day means that the chances of a bigger one soon are now finite but quite small," Heaton said.

However, he warned that California, criss-crossed by faults including the notorious San Andreas Fault and the smaller San Simeon Fault that was at the origin of Monday's quake, was still expected any time.

"The big earthquakes are definitely coming, but for every magnitude eight (quake), we get 10 sevens, and for seven we get 10 sixes, so we will have a lot of events of this size before the really big ones come."

The epicentre of Monday's quake was near the coastal town of San Simeon, about 57 kilometers (36 miles) from the site of the worst damage. Paso Robles' old brick buildings proved far more vulnerable that the wooden structures in other towns in the largely rural area.

Emergency services and building experts were inspecting the remaining upright parts of the building that collapsed after its roof was hurled off and about 80 other buildings in the town for safety.

"We have to make sure that none of these structures poses a threat to public safety," said police spokesman Clint Ballard.

The two fatalities of the quake were two women, aged 55 and 19, who were struck by the roof of the 116-year-old building in which they worked as it slid into the street.

The rubble crushed a row of cars and sent masonry and timber flying across the centre of the town of 27,000 people, police said. Miraculously no-one else was trapped.

Schwarzenegger was expected to meet local and emergency services officials as well as survivors of the disaster when he tours the region.

Telephone lines to the stricken area were jammed for hours after the quake and power to a reported 40,000 homes was cut in the wake of the temblor.

"It was really frightening yesterday and because of the aftershocks through the night, a lot of people are still real nervous," said Paso Robles hotel worker Brandy Wilson.

TERRA.WIRE