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 eight 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.

Snow fell throughout Wednesday, from the Great Lakes region into New England; as much as 24in (60cm) was forecast in the state of Wisconsin, and 6in in Illinois.

States of emergency have been declared in the Midwestern states of Wisconsin, Michigan and Illinois, and even in the normally warmer Deep South states of Alabama and Mississippi.

"This could possibly be history-making," said Ricky Castro, a National Weather Service (NWS) meteorologist in Illinois.

Dangerous wind chills across the Upper Midwest and into the Ohio Valley were expected to last through Thursday, with heavy snow downwind of the Great Lakes, the NWS said.

Heavy rain and mountain snow were expected in the west of the country by the weekend, it added. (BBC)