A once-in-a-generation winter storm with temperatures as low as -40 degrees has hit the U.S., AFP reports.

According to the American Automobile Association, blinding whiteout and dangerous road conditions have already begun to spread.

The main northbound I-90 freeway has been closed in South Dakota, and officials said it would not reopen until Friday.

Heavy snowfall and howling winds disrupted vacation plans during one of the busiest times of the year, when a huge cold front swooped in from the Arctic and froze downtown.

Meteorologists said it was so cold in some places that anyone who went outside risked freezing within minutes.

Several highways are currently on the "impassable roads" list.

Flightaware.com, the plane tracking website, showed that more than 22,000 flights were delayed Thursday, with 5,500 flights completely cancelled.

AccuWeather forecasters said the storm could quickly turn into what is known as a "bomb cyclone" through a process known as "bombogenesis," where atmospheric pressure drops and a mass of cold air collides with a mass of warm air.

The National Weather Service has warned that snowstorms lasting an hour or two have already occurred or are expected from the Central Plains to the mid-Atlantic and Northeast.