More than 200 million people are under weather warnings or advisories on one of the busiest travel days of the year in the United States and Canada.
Some 1.5 million are without power as high winds cause blackouts.
Major airports have cancelled thousands of flights as the storm intensifies.
Forecasters have said temperatures could plunge as low as -70F (-57C) in some parts of the country.
Experts warn this could lead to frostbite within five to 10 minutes.