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.

The US city of Chicago has experienced extreme cold

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

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

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

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.

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

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

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

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

All images subject to copyright