The Arctic front sweeping across the United States has reportedly got so cold that the small town of Hell in Michigan has "literally frozen over".
According to Bloomberg News reporter, Derek Wallbank, temperatures have reached as low as -13C, with a wind chill of -33C.
The US National Weather Service has produced a graphic explaining the 'polar vortex' which has brought record low temperatures to many parts of the United States.
At least four people have been killed as an Arctic front continues to grip the United States bringing the coldest temperatures in two decades.
The weather-related deaths reported include a 48-year-old Chicago man who had a heart attack while shoveling snow on Sunday and an elderly woman who was found outside her Indianapolis home on Monday.
Five facts about the US cold snap:
- At -38C, Babbitt, Minnesota has been colder than Mars in recent days. It was also the coldest place in the United States on Monday according to the National Weather Service.
- People have been warned frostbites could set in on uncovered skin within minutes if they go outside.
- Some 4,000 flights were canceled and 7,500 delayed, according to FlightAware.com, which tracks airline activity.
- Temperatures were 11 to 22C below average in parts of Montana, North and South Dakota, Minnesota, Iowa, Wisconsin, Michigan and Nebraska.
- The coldest temperatures in years and gusty winds were expected as far south as Brownsville, Texas, and central Florida, the National Weather Service said.
A blast of Arctic air that has gripped the vast middle of the United States has forced a polar bear at a Chicago zoo indoors, according to local media reports.
Anana, a polar bear at Lincoln Park Zoo has not yet grown a layer of blubber that bears need to insulate themselves against arctic winter temperatures and will be staying warm inside a “climate-controlled” area.
"In the wild, they would seasonally eat seals and fatten themselves up with that blubber," Lincoln Park Zoo spokeswoman Sharon Dewar told CNN.
But zookeepers "don't feed them seals or fatten them up," she said.
The U.S. cold snap outdid freezing weather in Almaty, Kazakhstan, where it was -22C and Mongolia at -23C.
More than half the flights at Chicago's O'Hare International Airport were canceled as fuel supplies froze, leaving crews unable to fill aircraft tanks. The afternoon temperature in Chicago yesterday dipped to minus -24C.
There is a high chance of more snow in the Great Lakes region of the US where temperatures remain at a record low, according to the National Weather Service.
Cities in the region have been blanketed in snow as a so-called polar vortex - an area of cold air that normally hovers over the polar region - was pushed south over Canada and the US.
The National Weather Service has warned that the "dangerously low temperatures" will persist in many parts of the US on Tuesday.
The weather system is beginning to creep eastwards but temperatures will remain on average around 20 degrees (Fahrenheit) below where they should be for the time of year.
NBC News reports that Hawaii is the only state in the country that is not affected by freezing temperatures.
US train operator Amtrak is reporting disruptions to its north-east services due to the extremely low temperatures.
Due to extreme cold forecasted to impact the Northeast, #Amtrak will operate a modified schedule on the NEC & Empire Line on Tues, Jan.7.
Services have been suspended between Philadelphia and Baltimore, although it was not clear if this was weather-related.
Acela/Northeast Regional service is temp suspended btwn PHL/BAL due to mechanical problems involving the overhead electrical system.
More than 9,000 flights have been cancelled in the US in the past four days as a result of the severe weather and record low temperatures, Bloomberg reports.
Most of the cancellations were in the Chicago airport, with O’Hare International and Midway International accounting for 1,500 cancellations.
Around 3,364 flights were cancelled and 3,155 delayed due to plummeting temperatures in the US, FlightAware.com reported.
Major US airline JetBlue Airways today grounded flights for 17 hours at four of the busiest airports in the country.
More than half of the flights in or out of Chicago's O'Hare International Airport were cancelled after temperatures in the Windy City plunged to -15.