Seven US states have declared a state of emergency due to a winter storm.

BBC News says over 60 million people are being affected by extreme weather caused by a polar vortex – an area of cold air that circulates around the Arctic.

The winter storm could bring the heaviest snowfall and coldest temperatures in over a decade.

A state of emergency has been declared in Kansas, Missouri, Kentucky, Virginia, West Virginia, Arkansas and parts of New Jersey.

Thousands of flights have already been delayed or cancelled, with many roads cut off and schools shut as a result of the storm.