Des Moines, Iowa – A big freeze gripped swathes of the US on Friday, jamming transport and dumping heavy snow across the north, including in Iowa, where Republican Party presidential hopefuls are in the final stretches of caucus campaigning. It also threatened the NFL playoffs, which are set to kick off.

Forecasters warned "dangerously cold Arctic air" and blizzards would affect millions of people in the north, with temperatures to plunge as low as -40 Fahrenheit, with windchill making it feel even colder in some places.

The extreme weather was making life difficult for White House hopeful Ron DeSantis and his rival Nikki Haley, who both canceled events just days before the Iowa caucus vote – the first of the 2024 White House race.

"We want everyone to be safe," DeSantis told reporters outside his Des Moines headquarters.

"We’ve had to rearrange the schedule but we’re working hard."

Haley implored Iowans not to let the brutal cold prevent them from voting on Monday in the first statewide test of who will take on the party's presidential mantle.

"I know it’s going to be negative 15 on Monday. I don’t even know what that is. I literally can’t comprehend it... But I’m going to be out there and I want you to go out there," Haley said Thursday.

Despite a quickening competition between the two, both trail former president Donald Trump by a huge margin in the race for the Republican Party nomination.

Several inches of snow were expected across Iowa throughout Friday, with the National Weather Service warning of dangerous conditions on the roads.

"Travel may become impossible," the NWS said. Hazardous travel to continue through Saturday across much of central Iowa."

"Dangerous cold temperatures will accompany this storm, adding an extra layer of risk to travel."

Images posted on social media showed whiteout conditions in Nebraska and Iowa, as authorities warned accidents and low visibility were causing lengthy delays.

The NWS said parts of the Northern Plains would log record lows over the coming days, approaching -40 F with howling winds making it feel as low as -50 F.

"Wind chills of this nature can lead to frostbite on exposed skin within minutes," the agency warned.

More than 2,700 flights were canceled across the country, including over 400 at Chicago's O'Hare Airport, according to flightaware.com, which maps travel misery. Tens of thousands of other passengers faced delays.

The winter weather was threatening key football games over the weekend, as the NFL enters its post-season.

The Kansas City Chiefs will host the Miami Dolphins on Saturday night at their Missouri home, with conditions expected to be bitterly cold. While the Chiefs and their star quarterback Patrick Mahomes are accustomed to extreme weather, his Dolphins opponent, QB Tua Tagovailoa, is more used to the balmy weather of Florida.

Sub-zero temperatures were also expected to afflict the Pittsburgh Steelers' visit to Buffalo, where they take on the Bills in another win-or-go-home game.

The western US was also expected to get hit with heavy snow, as a storm system collides with freezing Arctic air.

Forecasters said there could be considerable accumulation over parts of Oregon, Idaho, and Utah.

The storms come on the heels of severe cold weather that slammed much of the US earlier this week, causing several deaths and knocking out power to hundreds of thousands of homes and businesses.