The US weather agency has issued a "life-threatening" flash flood warning for the Ohio and Tennessee valleys, particularly in western Kentucky and Tennessee.

Widespread heavy rain is expected throughout the day and into the night, significantly increasing the risk of dangerous flash flooding, the National Weather Service (NWS) said in a statement on Saturday.

The greatest threat extends from Tennessee into western and central Kentucky, but surrounding areas in the Ohio Valley are also at risk.

In addition to the flooding risk, winter weather is expected to hit Michigan, New England, and the northeast US this weekend, with heavy snow, sleet, and freezing rain creating hazardous conditions.

Some areas are likely to see enough icing to cause power outages, the weather agency warned.