An unusually heavy winter storm marched across the nation's mid-section, heading east on Tuesday, threatening roughly two-thirds of the country with what forecasters said could be up to 30 centimetres of snow.

The storm system forced the closing of many state offices and schools in hard-hit Kansas, where Gov. Sam Brownback declared a state of "disaster emergency." Authorities in Kansas and neighbouring Missouri advised residents to stay in their homes and the National Weather Service warned of "extremely difficult travel conditions."

Interstate 70, a key road artery connecting Kansas City and St. Louis, Mo., was closed in both directions for part of the day Tuesday near Columbia, Mo., after poor visibility and slippery conditions caused several tractor-trailers to collide, according to the Missouri State Highway Patrol.

'It's remarkable weather. Winter is entrenched. It doesn't appear to be wanting to go anywhere.'- Greg Carbin, NWS Storm Prediction Center

Numerous additional accidents were reported in Missouri as cars skidded off slick highways, the state patrol said.

Ten to 17 centimetres of snow had fallen in the Kansas City area by late afternoon, with more expected before the system tapers off early Wednesday, according to the NWS.

"Kansas City and eastern Kansas is going to get a lot of snow," said Greg Carbin, meteorologist for the NWS Storm Prediction Center. "It's remarkable weather. Winter is entrenched. It doesn't appear to be wanting to go anywhere."

The heavy snow and ice tracking through the central United States was headed north-east into Pennsylvania, New York and New England, forecasters said.

Areas from the lower Great Lakes eastward through central New England should see a foot or more of snow before the system moves out to sea by Wednesday night, according to the NWS, and heavy rains could result in flooding across the Tennessee Valley and Ohio Valley.

Nearly 8,000 flights were delayed across the country on Tuesday afternoon, and more than 1,640 were cancelled, according to Flightaware.com, a website that tracks air traffic.

Multiple accidents reported

The storm set up Monday night over southwestern Kansas and was peaking over Kansas City on Tuesday.

APTOPIX Winter Weather Kansas

A bicyclist crosses Douglas Avenue in downtown Wichita, Kan., during a heavy snowstorm on Tuesday. (Travis Heying/The Wichita Eagle/Associated Press)

This event is uncommon, said NWS meteorologist Dan Hawblitzel, as only about three per cent of the winter storms that hit Kansas City total more than 15 centimetres of snow.

Connecticut Gov. Dannel Malloy postponed his state of the state address. He said the impending storm was also causing state legislative leaders to push back by a day the start of the joint legislative session.

"While I hope the storm is not as bad as predictions suggest, I also don't want to put anyone in harm's way," Gov. Malloy said in a statement announcing the delay.

Schools in Providence, R.I., were ordered closed Wednesday.

Icy conditions were wreaking havoc in Arkansas early on Tuesday, with multiple accidents reported on major traffic arteries, said Arkansas highway officials.

The most hazardous conditions were reported in the northwestern corner of the state, near the Missouri and Oklahoma borders.

Arkansas Gov. Mike Beebe directed that only "essential" state employees were to report for work in the Little Rock area.

The incoming snow comes after a fast-moving winter storm hit the U.S. Northeast on Monday, forcing flight cancellations throughout the region and tying up road traffic the day after the NFL's Super Bowl championship game in New Jersey.

On Sunday, the famed groundhog Punxsutawney Phil emerged from his burrow in the small Pennsylvania town, saw his shadow and — as the legend goes — predicted six more weeks of winter.

2 deaths

At least two deaths and one serious injury were blamed on the storm.

Winter Weather Missouri

A salt truck clears the road eastbound along Broadway during a winter storm on Tuesday in Columbia, Mo. A winter storm bore down on Missouri Tuesday, dumping enough snow to make roads treacherous and forcing the cancellation of dozens of flights and hundreds of schools. (Ryan Henriksen/The Columbia Daily Tribune/Associated Press)

In western Kentucky, where the snow began falling Sunday, a 24-year-old man died that night when his car skidded into a snowplow. On Monday, a 73-year-old New York City man was fatally struck by a backhoe that was moving snow.

A 10-year-old girl was in serious condition after she was impaled by a metal rod while sledding north of Baltimore.

In Ohio, where the storm dumped as much as 25 centimetres on the state Monday, there were numerous traffic accidents, none serious.

"It was mostly bent fenders and hurt feelings," said Kim Carver, director of the Scioto County Emergency Management Agency in Portsmouth.

With files from The Associated Press