In many places, like Chicago, the temperatures climbed just above zero on Friday after the city reeled under intense cold with temperatures dipping to extreme lows like minus 31 degrees Celsius, The New York Times reported.

"It's fairly rare to see this much of a turnaround in temperature in this sort of time," said Todd Kluber, a meteorologist with the National Weather Service.

Many offices and school reopened in the Midwest which comprises the states of Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota and Wisconsin.

But the warm-up was expected to take a jarring jump in the coming hours and days - sending the battered region into a temperature roller coaster.

The fast-rising temperatures were also causing a new set of risks to contend with, including possible flooding, abundant potholes and clogged storm water drainage systems, The New York Times reported.

In Wilmington, Illinois, along the Kankakee River, the Police Department warned of flash flooding "that may occur without any warning" as ice moved downstream.

The Midwest's deep freeze was brought by the Polar Vortex, a mass of cold air that is normally contained above the North Pole but in recent weeks broke apart, sending a block of icy air toward the US.

According to officials, the 29 victims included a 72-year-old woman who was found unresponsive in her garage on Friday in Germantown Hills, Illinois, a University of Iowa student, a woman who froze to death inside a Milwaukee apartment after the thermostat malfunctioned and a man who died while using a snowblower in Buffalo.

Stathis Poulakidas, a burn surgeon at Chicago's John H. Stroger Jr. Hospital of Cook County, said nearly 50 patients had sought treatment for frostbite in recent days, about half of them homeless.