In pictures: Polar vortex strikes North America

Temperatures have plunged to -30C (-22F) and below in parts of North America as extreme cold weather known as a polar vortex strikes the region.

At least eight people are reported to have died in incidents related to the weather.

Image source, Getty Images

Image caption, The US city of Chicago has experienced extreme cold

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Image source, Reuters

Image caption, So low are the temperatures that some residents have been posting images of themselves throwing boiling water into the air and seeing it turn instantly into ice

Image source, Reuters

Image caption, Temperatures of -37C were recorded in North Dakota. Here, trucks are seen amid icy conditions near the city of Fargo

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Image source, Reuters

Image caption, People in Chicago and elsewhere have been told to stay indoors if they can

Image source, Getty Images

Image caption, Those who have braved the elements, such as this commuter in downtown Chicago, have wrapped up as warm as they can

Chicago is also using fire to melt snow on the railway in order to keep the trains running.

Image source, Reuters

Image caption, The freezing temperatures in the Great Lakes region between the US and Canada have led to the formation of "cloud streets" - parallel rows of cumulus clouds streaming over the lakes' surface as seen in this US weather satellite image

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Image source, AFP

Image caption, Parts of the Niagara Falls in Ontario, Canada, have frozen

Image source, AFP

Image caption, Also in Ontario, the city of Kingston has seen snowfall. Wind chill temperatures were forecast to be about -30C on Thursday

Image source, AFP

Image caption, The cold snap is now reported to be edging eastwards. Here, the Canadian city of Montreal is seen blanketed in snow

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