The US will shiver this week in a once-in-a-generation deep freeze, forecasters warn.

The most extreme arctic blasts, caused by a spinning pool of cold air known as the polar vortex, could bring temperatures as low as -53C (-64F).

Weather officials in the state of Iowa have warned people to "avoid taking deep breaths, and to minimise talking" if they go outside.

At least 55 million people are forecast to experience below zero temperatures.

A state of emergency has been declared in the Midwestern states of Wisconsin, Michigan and Illinois as well as in the normally more clement southern states of Alabama and Mississippi.

John Gagan, a National Weather Service (NWS) meteorologist, said: "The intensity of this cold air, I would say, is once in a generation."

The NWS is warning that frostbite is possible within just 10 minutes of being outside in such extreme temperatures.

The coldest temperatures are expected to hit from Tuesday to Thursday, with forecasters predicting that Chicago will be colder than Antarctica.

The Illinois city could experience a low of -33C (-27F), with freezing winds making that feel closer to -46C (-50F), officials say. As much as 2ft (60cm) of snow is forecast in Wisconsin, and 6in is expected in Illinois. Alabama and another southern state, Georgia, are expecting snow, too.

Forecasters are attributing this cold snap to a sudden warming above the North Pole, caused by a blast of hot air from Morocco last month.

Source: BBC