US polar vortex: What's its like in Chicago when it's -30 degrees?

Video caption, US weather: Chicago kids tell us what it's like during a Polar vortex

You might think it's been pretty cold here in the UK recently, but in parts of America it's been even cooler.

A polar vortex - a spinning pool of cold air - has caused temperatures to drop to below -20 degrees in some parts of the US Midwest.

Millions of people have been warned not to go outside because of the extreme temperatures, with schools closed and cities all but shut down.

The cold weather has also caused lots of travel problems, with some flights cancelled or delayed, while snow and ice has built up on roads.

At least eight people have died because of the severely cold weather.

成人快手 reporter Harry Low is in Chicago where temperatures have dropped to -30 degrees.

He tried out a stunt in which you throw boiling water in the air and it freezes instantly.

DON'T TRY THIS AT HOME. It could be dangerous and only works in extremely low temperatures.

Video caption, It's -30 degrees in Chicago - cold enough for boiling water to freeze!