More than 70 million Americans are under winter weather alerts as a huge winter storm is forecast to bring the heaviest snowfall and coldest temperatures in over a decade.

Thirty states are under weather alerts in an area spanning 1,500 miles (2,400km) from Kansas to the East Coast, the National Weather Service (NWS) said.

A state of emergency has been declared in Kentucky, Virginia, Kansas, Arkansas and Missouri. Parts of the US unaccustomed to severe cold, including Mississippi, Texas and Florida, have been warned to expect treacherous conditions.

Forecasters say the extreme weather is being caused by the polar vortex, an area of cold air that circulates around the Arctic.

The storm has already hit the Central Plains and is expected to arrive at the US east coast by Sunday evening.

Parts of upstate New York have experienced at least 91cm (3ft) of snow so far.

Washington DC is bracing for between 5-9in (0.4-0.75ft) of snow, while Philadelphia could get 2-4in (0.1-0.3ft).

Nearly four million people are under blizzard warnings in Kansas and Missouri, where wind gusts of 40mph were projected.

Parts of Kansas and Missouri are expected to see anywhere between 4-14in (0.3-1.6ft) of snow, and Indiana could see up to 9in (0.75ft).

“For some, this could be the heaviest snowfall in over a decade,” the National Oceanic and Atmospheric Administration said.

AccuWeather forecaster Dan DePodwin said: “This could lead to the coldest January for the US since 2011.”

He added that “temperatures that are well below historical average” could linger for a week.

Severe travel delays are expected.

Conditions on roads have deteriorated, with crashes involving lorries and cars, as well as a fire engine rolling over near Salina, Kansas.

In the central US, there will be “considerable disruptions to daily life” and “dangerous or impossible driving conditions and widespread closures” on Sunday, according to the NWS.

“Whiteout conditions will make travel extremely hazardous, with impassable roads and a high risk of motorists becoming stranded,” the NWS warned.

Portions of the southern US including Arkansas, Louisiana and Mississippi, may see severe thunderstorms.

Private meteorologist Ryan Maue said: “It’s going to be a mess, a potential disaster. This is something we haven’t seen in quite a while.”

American, Delta, Southwest and United airlines are waiving change fees for passengers because of the potential flight disruptions.

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