Emergency workers scrambled Monday to stabilise a California levee after a breach forced thousands from their homes, as another major storm loomed, threatening more flooding.

Houses were inundated and vehicles submerged when the Pajaro River burst over a crumbling levee overnight Friday into Saturday, with firecrews going door-to-door to rouse sleeping residents.

"Emergency temporary repair work to stabilize the breach is underway," the county said in a statement.

"Flood waters are moving through the community and southward. Residents who have not left the area are still encouraged to do so."

Rescue teams, including divers, were working in the region, the county said, although no deaths or injuries have been reported.

More than 10,000 people throughout the county have been told to leave their homes because of the Pajaro River and nearby Salinas River, which is also expected to flood over the coming day.

The area was hit by flooding in January as a long line of atmospheric rivers -- ribbons of moisture that run through the atmosphere -- dumped trillions of gallons (liters) of water on California.

"People are taking it seriously," she was quoted as saying by the San Francisco Chronicle.

"This is real. Mother Nature is fickle. It's a holy moly situation."

Meteorologists said that while rain had eased off, it would be back late Monday and into Tuesday, with more than two inches (five centimeters) expected on ground too wet to absorb any more water.

Brooke Bingaman, lead meteorologist for the National Weather Service (NWS) in the Bay Area and Monterey Bay, said the danger of more flooding was very real.

"It is critical that you leave areas that are expected to be impacted," she said in a video posted to Twitter.

"Remember, it's better to stay the night in a strange place than to wake up to rising water in your home or to realize that you've been cut off due to closed roads all around you."

The parade of winter storms that have pummeled California have caused hundreds of millions of dollars of damage as they washed out communities, brought down power lines and caused landslides.

More than 20 people have died.

Mountainous areas have seen near-record snowfall over the winter months, leading to huge snowpacks and fears that relatively warm rain now could cause a huge melt that will overwhelm watercourses.

Meteorologists said the atmospheric river flowing over the US West from Monday night would exacerbate that risk.

"Additional heavy rain and snowmelt will result in more widespread flooding from Tuesday into Wednesday, particularly in low elevations and areas with increasing temperatures impacting snowpack," the NWS warned.

"Creeks and streams will continue to be vulnerable to flooding from additional rain and snowmelt," the agency said, predicting several feet of heavy snow over the Sierra Nevada range.

On the other side of the country, New York state was bracing for heavy snowfall from a storm forecast to pack 100 km/hour winds and potential to knock out power.

Governor Kathy Hochul declared a state of emergency Monday night, saying the storm could be deadly, and urged people not to travel on Tuesday.