The dangerously low temperatures that hit the northern parts of United States killed at least 26 people in eight states, while hundreds of people have been admitted to hospitals with frostbites, fractures, heart attacks, reported AP on Saturday.

The bitter cold was caused by a polar vortex, which is a stream of cold air that spins around the stratosphere over the North Pole. The vortex’s current was disrupted and pushed south into the United States. Cotton in Minnesota recorded the lowest temperature at -48 degree Celsius on Thursday based on preliminary data, reported BBC.

In Illinois state, hospitals reported more than 220 cases of frostbite and hypothermia since Tuesday, the day the polar vortex moved in and overnight temperatures dropped to minus 34 degree Celsius or lower.

In Michigan, a 90-year-old woman died of hypothermia after locking herself out of her home while one motorist died during a snowstorm on Friday after striking a truck that was parked on the side of the road in central Indiana. A few others after freezing outdoors or in unheated homes or while shovelling snow.

The cold has now retreated, but the temperature is expected to rise to 26 degree Celsius by early next week in some regions, The Guardian reported quoting forecasters. Experts said the rapid thaw is unprecedented, and could lead to pipes bursting, rivers flooding and crumbling roads.

“That cold air that was over the Great Lakes, over the Midwest, has shifted off,” said Bryan Jackson, a National Weather Service meteorologist, according to ABC. “Now the high pressure is over Pennsylvania and New York…as it moves east, it’ll bring in air from the south and we do expect it to warm up over the weekend.”

At least 50 million people were likely to have been affected as large expanses extending from Dakotas in the midwest to western Pennsylvania had received weather warnings.