On Thursday, the National Weather Service warned people in the US Midwest that they should stay in as even five minutes of exposure could cause frostbite.

The Midwest is in the grip of the Polar Vortex that has sent temperatures to record lows. Schools and universities were shut in the region and the all-weather US Postal Service stopped deliveries.

More than 1,000 flights were cancelled on Wednesday throughout the Midwest. “It’s just a dangerous cold,” said National Weather Service meteorologist Butch Dye.

Temperatures are expected to rise by Friday but disruptions caused by the cold will persist, including power outages and cancelled flights and trains.

Crews in Detroit will need days to repair water mains that burst Wednesday, and other pipes can still burst in persistent sub-zero temperatures.

Before the worst of the cold begins to lift, the National Weather Service said Chicago could hit lows early Thursday that break the city's record of -27F (-32 Celsius) set on January 20, 1985.

Some nearby isolated areas could see temperatures as low as minus -40F (-40C).

As temperatures bounce back into the single digits on Thursday and into the comparative balmy 20s by Friday, more people were expected to return to work in the nation’s third-largest city, which resembled a ghost town after most offices told employees to stay home.

At least eight deaths were linked to the deep freeze, including an elderly Illinois man who was found several hours after he fell trying to get into his home and a University of Iowa student found behind an academic hall several hours before dawn.

Additional details from AP