More than 60 million Americans are under the grip of a major winter storm that could bring the heaviest snowfall and coldest temperatures in more than a decade, the BBC reports.

States of emergency have so far been declared in seven states, in Kansas, one of the hardest-hit areas, Missouri, Kentucky, Virginia, West Virginia, Arkansas and parts of New Jersey.

Forecasters say the extreme weather is being caused by a polar vortex - an area of ​​cold air that circulates around the Arctic - bringing cold weather to parts of the central US.

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