Much of the US faced another round of biting winter weather on Sunday, with torrential rains causing intense flooding in Kentucky and resulting in multiple deaths.

The Kentucky governor, Andy Beshear, on Sunday said at least eight people were dead amid the inundation, with the number possibly increasing.

Among the dead was a 73-year-old man found in floodwaters in Clay county, Kentucky, WKYT-TV reported. The Clay county emergency management deputy director, Revelle Berry, confirmed the fatality but did not provide additional details.

Meanwhile, in Hart county, Kentucky, the state department of fish and wildlife said an investigation into a death and a rescue operation was under way, WNKY-TV reported. The station reported a youth died and a second victim was missing in flooding on Saturday evening.

The fish and wildlife department and the Hart county sheriff’s office did not immediately respond to a request for more information from the Associated Press.

Severe storms also swept through parts of Florida and Georgia, where tornado watches were in effect early on Sunday, the National Weather Service (NWS) said.

Elsewhere, bone-chilling cold is expected for the northern plains with low temperatures into the -30s F near the Canadian border. Dangerously cold wind chill temperatures in the Dakotas and Minnesota of -40F (-40C) to -50F are expected.

Heavy snowfall amounts were expected in parts of New England and northern New York. In some areas, wind gusts could reach 60mph (about 97km/h) and create “hazardous whiteout conditions”, the NWS said.

In Kentucky, water submerged cars and buildings – and mudslides blocked roads in Virginia. Both of the states were under flood warnings, along with Tennessee and Arkansas. The NWS warned residents to stay off the roads.

Beshear said at least 146 national guard members were helping rescue people from floodwaters in that state. Similar rescues were reported in Rives, Tennessee, after the failure of a levee along the Obion River there.

The Kentucky governor pre-emptively declared a state of emergency in Kentucky. He also said that he had written to Donald Trump’s White House requesting an emergency disaster declaration and federal funds for affected areas.

The president had approved the request, the Kentucky congressman James Comer said.

“We want to specifically put assets in places that flood and have flooded in the past,” Beshear said on social media.

He said shelters were opening in Pike county and Jenny Wiley state resort park in Prestonsburg.

The Kentucky River medical center in the city of Jackson said it had closed its emergency department and was transferring all patients to two other hospitals in the region. The hospital said it would re-evaluate conditions on Sunday morning to determine when it can safely reopen. The north fork of the Kentucky River was forecast to crest nearly 14ft (4.3 metres) above flood stage that afternoon, the weather service said.

Flash flooding hit some roads in Bowling Green, and parts of western Kentucky could face up to 8in (20cm) of rain.

Meanwhile heavy snow was expected to blanket much of New England and then transition to sleet, making travel nearly impossible. The heaviest accumulations, possibly a foot or more, were expected in upstate New York and portions of northern New England.

Snow and Arctic temperatures swept much of the midwest and upper plains, covering roads in eastern Nebraska, northern Iowa and much of Wisconsin. Winter weather advisories were issued for parts of those states and Michigan, with up to 4in of snow predicted throughout Iowa, southern Wisconsin and most of Michigan by Sunday evening.

Meteorologists said the US was about to get its 10th and coldest polar vortex stretching event this season, with the northern Rockies and northern plains first in line. Weather forces in the Arctic are combining to push the chilly air that usually stays near the north pole into the US and Europe.

In Denver, where temperatures were expected to dip as low as 14F over the weekend, the city opened shelters for those living on the streets.

Dry weather returned to southern California after the strongest storm of the year. But the risk of rock and mudslides on wildfire-scarred hillsides continued because dangerous slides can strike even after rain stops, particularly in areas where vegetation that helps keep soil anchored has burned away.

Water, debris and boulders rushed down the mountain in the city of Sierra Madre on Thursday night, trapping at least one car in the mud and damaging several home garages with mud and debris. Bulldozers cleaned up mud-covered streets in the city of 10,000 people.

A storm in the Sierra Nevada dumped 6ft of snow over 36 hours. Two Mammoth Mountain ski patrol workers were injured in an avalanche during avalanche mitigation work on Friday, the resort said on Facebook.

Guardian staff contributed reporting