A deep freeze expected in the US Midwest, north-eastern New England states and the South could break records amid heightening fears of frostbite and hypothermia.

Preceded by snow in much of the Midwest, the frigid air began to spread across the country on Saturday and will and extend into early next week, funnelled as far south as the Gulf Coast. It is being blamed on a "polar vortex" as one meteorologist calls it, a counterclockwise-rotating pool of cold, dense air.

"It's just a large area of cold air that comes down, forms over the North Pole or polar regions ... usually stays in Canada, but this time it's going to come all the way into the eastern US," said National Weather Service meteorologist Phillip Schumacher in Sioux Falls, South Dakota.

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The forecasts were for minus 31ÚC in Fargo, North Dakota, minus 35ÚC in International Falls, Minnesota, and 26ÚC below in Indianapolis and Chicago. At those temperatures, exposed skin can get frostbitten in minutes and hypothermia can set in.

Parts of the north-eastern New England states dropped into the negatives early on Saturday, with East Brighton, Vermont, seeing 34.4 below zero ÚC just after midnight and Allagash, Maine, hitting minus 37.8ÚC. The cold will sweep through other parts of New England where residents are digging out from a snowstorm. Snow will reduce the sun's heating effect, so night lows will plummet.

By today, western and central Kentucky could be struggling with temperatures at minus 18ÚC - "definitely record-breaking", said meteorologist Christine Wielgos in Paducah, Kentucky. And in Atlanta, tomorrow's high is expected to hover around minus 4ÚC.