Treacherous snow and freezing rain have struck the northeastern US, disrupting thousands of flights and causing traffic chaos for millions of Americans.

A state of emergency was declared in the states of New Jersey and New York, where dwindling reserves of salt – used to melt snow and road ice – was a problem.

By late January, New Jersey had already used 277,000 tonnes of salt, 18,000 more than during the entire previous winter.

Connecticut Governor Dannel Malloy on Wednesday ordered all non-essential employees to stay home and a number of schools were also closed.

Huge snowfall was expected across a swath of the northeastern of the country, arriving in New England from the central US. Snow will be followed in several places by freezing rain, forecasters say.

More than 2400 arriving and departing flights were cancelled on Wednesday, with more than 1280 others delayed.

Hardest hit were airports in Boston, New York and Chicago.

Weather forecasters have warned that yet another winter storm is liable to hit at the weekend.