Cities are all but shutting down across the US Midwest as the region shivers in a deadly cold snap known as a polar vortex.
At least seven people have been killed in several states as a result of the arctic weather. Temperatures fell to -30C (-22F) in Chicago - colder than parts of Antarctica - and -37C in North Dakota.
Freezing weather will chill 250 million Americans, and 90 million will experience -17C (0F) or below.
