At least nine people have died as wild weather rocked the US, with the state of Kentucky recording the lion’s share of fatalities as waterways swelled from heavy rain and submerged roads.

Kentucky Governor Andy Beshear said on Sunday that hundreds of people stranded by flooding had to be rescued.

Beshear said many of the deaths, including a mother and seven-year-old child, were caused by cars getting stuck in high water.

“So folks, stay off the roads right now and stay alive,” he said.

“This is the search and rescue phase, and I am very proud of all the Kentuckians that are out there responding, putting their lives on the line.”

Beshear said the storms have knocked out power to about 39,000 homes, but he warned that harsh winds in some areas could increase outages.

Much of the US beyond Kentucky faced another round of biting winter weather.

The Northern Plains faced life-threatening cold, and tornado watches were issued for parts of Georgia and Florida.

In southeastern Kentucky, a 73-year-old man was found dead in floodwaters in Clay County, County Emergency Management Deputy Director Revelle Berry said.

Parts of Kentucky and Tennessee received up to 15 centimetres of rain during the weekend storms, said Bob Oravec, a senior forecaster with the National Weather Service.

“The effects will continue for a while, a lot of swollen streams and a lot of flooding going on,” Oravec said on Sunday.

“Any time there’s flooding, the flooding can last a lot longer than the rain lasts.”

In Atlanta, a person was killed when an “extremely large tree” fell on a home early on Sunday, according to Atlanta Fire Rescue Captain Scott Powell.

Elsewhere, bone-chilling cold is expected for the Northern Plains. Dangerously cold wind chill temperatures in the Dakotas and Minnesota of minus 40 Celsius to minus 45.6 C are expected.

Heavy snowfalls were expected in parts of New England and northern New York.

—AAP