Bitterly cold air from Siberia has brought dangerously frigid and likely record-setting temperatures to the eastern half of the US.
Temperatures are 20 to 40 degrees F below normal for February from the Mid-Atlantic to the South.
Schools in Chicago have closed and trains in the north-east corridor have been affected by the cold.
Extreme cold warnings are also in effect in the Canadian provinces of Ontario and Manitoba.
Frigid temperatures are expected to continue into Friday.
Record lows have already been broken in Kentucky, where it was -8F (-22C) on Thursday morning in Paducah and most of state was below 0F.
Weather forecasters believe the cold air will help break more than 100 daily record lows, NBC News reports.
Forecasted Highs/Lows in the eastern US:
- Atlanta, Georgia: 29F/14F
- Chicago, Illinois: 6F/-1F
- Nashville, Tennessee: 18F/7F
- Philadelphia, Pennsylvania: 20F/1F
- Raleigh, North Carolina: 21F/6F
- Washington, DC: 18F/2F
In Atlanta, temperatures dipped to 15F overnight and officials were trying to determine whether two people found dead had been killed by the cold.
The extreme cold is also threatening electricity grids in Tennessee - more than 30,000 lost power on Wednesday and officials are calling for residents to conserve energy as the state remains in an emergency footing.
Temperatures in the US capital of Washington DC are set to reach 2F, the lowest in 20 years.
Even Orlando, Florida, was expected to see temperatures fall below freezing.