NAPA, Calif. -- Ten seconds before a severe earthquake in California's wine country caused the ground to rumble throughout the San Francisco Bay Area, a university lab in the city of Berkeley got the alert that the seismic waves were rolling its way.

The lab is testing a prototype of an earthquake early-warning system that California is pursuing years after places like Mexico and Japan already have them up and running.

Sunday's rolling magnitude-6.0 earthquake in the Napa area has led to renewed calls for the system's quick deployment in the state before another, possibly more destructive temblor strikes.

"There's no doubt a major earthquake will hit California -- the only questions are when and where. I believe an integrated earthquake early-warning system is essential to save lives and property," California's senior senator, Democrat Dianne Feinstein, said in a statement Monday.

She joined a chorus of political leaders and scientists calling for the system. Experts say it would allow trains to slow down or stop, power plants and factories to shut off valves, and schoolchildren to dive under desks to avoid falling objects, reducing injuries and damage.

In California, it may be closer to reality than most state residents realize. A bill signed by Gov. Jerry Brown last year ordered his Office of Emergency Services to develop a comprehensive statewide system and by 2016, identify sources of funding for it. It would cost an estimated $80 million.

Richard Allen, director of the University of California, Berkeley, Seismological Lab, said the 10-second alert his lab received estimated the quake at a magnitude-5.7. Berkeley is about 64 kilometres from the quake's epicenter and did not experience any damage, but 10 seconds could have made a big difference in a more violent temblor, he said. That time would allow people to find safety, he said.

Sunday's quake caused several injuries, left four mobile homes destroyed by gas-fed fires and damaged wineries, historic buildings and hotels. The damage has been estimated as high as $1 billion.

The area has experienced dozens of aftershocks since, the largest of which was a magnitude-3.9 quake that struck at 5:33 a.m. Tuesday about 11 kilometres south of Napa.

There were no calls reporting damage or injuries, but the quake did rattle already frayed nerves.

The early-warning systems can't predict quakes and are not effective at the epicenter, where the tremors go out almost simultaneously. The warning people receive -- a few seconds to tens of seconds -- depends on the distance from the epicenter.

Napa would have received, at most, a second of warning if California already had a system in place, said Thomas Heaton, a professor of engineering seismology at the California Institute of Technology.

Meanwhile, the city's business owners spent Monday mopping up high-end vintages that spilled from barrels and bottles and sweeping away broken glass in the rush to get the tourist hotspot back in shape for the summer's final holiday weekend. Government and tourism officials assessing its economic and structural impact encouraged visitors to keep flocking to the charming towns, tasting rooms, restaurants and spas that drive the Napa Valley economy.

The worst damage and disruption was confined to the city's downtown, where a post office, library and a 141-room hotel were among more than 160 homes and buildings deemed unsafe to occupy or enter. Two hotels and 12 wineries remained closed Monday, as well as gift shops, restaurants and other downtown businesses, said Clay Gregory, president of tourism organization Visit Napa Valley.

August, September and October grape harvest represents the busiest time of year for both the valley's 500 or so vintners and the visitors who come from all over the world to see them work.

Lisa Leff in San Francisco and Scott Mayerowitz contributed to this story.