At least 21 people were killed as a Polar Vortex continued to freeze the US Midwest, dipping temperatures to record lows in the region, the media reported.

The Polar Vortex, which is a large area of low pressure and cold air surrounding the Earth’s North and South Poles, arrived earlier this week and has for days disrupted life across the entire region, reports The New York Times.

The Midwest region comprises Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota and Wisconsin.

According to officials, the victims included a University of Iowa student, a woman found frozen to death inside a Milwaukee apartment after the thermostat malfunctioned and a man wgi died while using a snowblower in Buffalo.

On Wednesday, a low of minus 30.5 degrees Celsius was registered in Chicago, which also recorded wind chills, while the city of Rockford in Illinois saw temperatures plummet to minus 31 degrees Celsius on Wednesday, the National Weather Service (NWS) said.

Mount Carroll, Illinois, recorded minus 38 degrees Celsius on Thursday. If this confirmes, it would become the state’s record low, supplanting the previous record of minus 36.

The sustained cold taxed energy systems across the Midwest, leading to some power failures and urgent calls to customers to reduce the heat in their homes.

Many schools, businesses and restaurants remained shut on Thursday.

By Thursday evening, airlines had cancelled more than 2,300 flights in the US, according to FlightAware. On Wednesday, cancellations topped 2,700.

Throughout the Midwest, hospitals reported patients arriving with symptoms tied to the weather such as frostbite or hypothermia.