A dangerously frigid arctic air mass has gripped a vast expanse of the US ahead of what could be one of the coldest Christmas Days on record, as a looming winter storm threatens to upend travel plans for millions of Americans.

Leading into the holiday weekend, the impending storm was expected to bring blizzard conditions to the Great Lakes region, up to five centimetres of rain followed by a flash freeze on the East Coast, wind gusts of 100km/h and bitter cold as far south as the Mexican border.

As the storm took shape over the Great Lakes on Thursday, a weather phenomenon known as a bomb cyclone was expected to develop from a “rapidly deepening low-pressure” system, the National Weather Service said.

The cyclone could spawn snowfalls of 1.25 centimetres an hour and howling winds gusting to 100km/h from the Upper Midwest to the interior Northeast, producing blizzard conditions and near-zero visibility, the weather service said.

Combined with the arctic cold, wind-chill factors as low as minus 40 degrees were forecast in the High Plains, the northern Rockies and Great Basin, the NWS said. Exposure to such conditions without adequate protection can cause frostbite within minutes.

Power outages were likely, and the storm was expected to make travel by land or air precarious or impossible at times.

More than half of the Lower 48 states, from Washington state to Florida, were under winter weather alerts, including wind chill advisories affecting about 135 million people.

Parts of the Mid-Atlantic and Plains could endure Christmas Day weather that is near the coldest on record, according to the weather service.

The mercury was expected to fall to -9 degrees in Philadelphia on Sunday, near a previous low from 1943, while Sioux City, Iowa, could end up at -26 degrees, surpassing a record from the 1980s.

More than 3000 US flights scheduled for Thursday and Friday have been cancelled, including nearly 1000 departures and arrivals at two major airports in Chicago, according to flight-tracking service FlightAware.

-AAP