The biting cold in the United States Midwest has claimed at least 15 lives, The Associated Press reported on Friday, as the mercury began to rise again in most states.

Although many places remained painfully cold on Thursday, the deep freeze eased somewhat, and the system marched east. Frigid weather descended on an area spanning from Buffalo to Brooklyn.

In western New York, a storm that dumped up to 51 centimetres of snow gave way to sub-zero temperatures and face-stinging wind chills. In New York City, about 200 firefighters battling a blaze in a commercial building took turns getting warm on buses.

Rockford, Illinois, was at a record-breaking minus 35 degrees Celsius on Thursday morning but should be around 10C on Monday. Other previously frozen areas could see temperatures of 13C or higher.

Elsewhere, a bridge in the western Michigan community of Newaygo, 64 kilometres north of Grand Rapids was closed as the ice-jammed Muskegon River rose above flood stage. Officials in Buffalo, New York, watched for flooding on the Upper Niagara River because of ice.

Earlier on Thursday, several cities set record lows. Rockford saw a record low temperature of minus 35 C, on Thursday. Cedar Rapids, Iowa, set a daily record low of minus 34 C.

Chicago's temperature dropped to a low of around minus 30 C on Thursday, slightly above the city's lowest-ever reading of minus 32 C in January 1985. Milwaukee's low was minus 31 C, and Minneapolis recorded minus 31 C. Wind chills were lower still.

In Illinois, at least 144 people visited hospital emergency rooms for cold-related injuries over two days. Most of the injuries were hypothermia or frostbite, according to a spokesman for the state Department of Public Health.

Unprecedented shift in temperature could cause problems

Days after the arctic conditions, forecasts say that the region will seemingly swing into another season, with temperatures climbing by as much as 27C.

The dramatic warm-up will offer a respite from the bone-chilling cold that cancelled school, closed businesses and halted trains.

Experts say the rapid thaw is unprecedented, and it could create problems ─ potholes will appear on roads, and bridges will be weakened by the freeze-thaw cycle. The same cycle can crack water mains and homeowners' pipes. Scores of vehicles will be left with flat tires and bent rims.

In pictures: Life slowly comes to a halt as polar vortex grips the midwest regions of the US

"I don't think there's ever been a case where we've seen (such a big) shift in temperatures [in the winter]," said Jeff Masters, meteorology director of the Weather Underground firm. "Past record-cold waves have not dissipated this quickly. ... Here we are going right into spring-like temperatures."

Masters said the polar vortex was "rotating up into Canada" and not expected to return in the next couple of weeks. If it does return in late February, "it won't be as intense".

Joe Buck, who manages Schmit Towing in Minneapolis and spent about 20 hours a day outdoors this week responding to stranded vehicle calls, said he's already taking calls for Monday to deal with a backlog of hundreds of stalled vehicles.

"Sunday is going to be 39 degrees ABOVE zero," said Buck, who has had 18 trucks running around the clock in wind chills that dropped to minus 45C.

In Detroit, where some water mains are almost 150 years old, city workers were dealing with dozens of breaks, said Palencia Mobley, deputy director of the Detroit Water and Sewerage Department.

The thawing of the pipes can sometimes inflict greater damage than the initial freeze. Bursts can occur when ice inside starts to melt and water rushes through the pipe or when water in the pipe is pushed to a closed faucet by expanding ice.

In other signs that the worst of the deep freeze was ending, Xcel Energy on Thursday lifted a request to its Minnesota natural gas customers to temporarily lower their thermostats to ease concerns about the fuel supply.

The effect on the overall economy was not expected to be that large. "It only shows up marginally in the economic data," said Diane Swonk, chief economist at Grant Thornton, who ended up working from home because her offices in Chicago were shut because of weather.

Mark Zandi, chief economist at Moody's Analytics, said one reason the severe cold weather will have less impact is that, unlike a hurricane, people did not lose electric power. "People may be in their homes, but they can do things such as online shopping," Zandi said. "Life goes on. It is a disruption to daily life, but it is not a big hit to the economy."

Commuters who had to bundle up like polar explorers might just get by with a light jacket by next week.