(Updates snow totals, forecasts, flight information)
By Carey Gillam
KANSAS CITY, Mo., Feb 4 (Reuters) - 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 a foot (30 cm) of snow.
The storm system forced the closing of many state offices and schools in hard-hit Kansas, where Governor Sam Brownback declared a state of "disaster emergency." Authorities in Kansas and neighboring Missouri advised residents to stay in their homes and the National Weather Service (NWS) warned of "extremely difficult travel conditions."
Interstate 70, a key road artery connecting Kansas City and St. Louis, Missouri, was closed in both directions for part of the day Tuesday near Columbia, Missouri, after poor visibility and slippery conditions caused several tractor-trailers to collide, according to the Missouri State Highway Patrol.
Numerous additional accidents were reported in Missouri as cars skidded off slick highways, the state patrol said.
Four to seven inches 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 canceled, according to Flightaware.com, a website that tracks air traffic.
The storm set up Monday night over southwestern Kansas and was peaking over Kansas City on Tuesday.
This event is uncommon, said NWS meteorologist Dan Hawblitzel, as only about 3 percent of the winter storms that hit Kansas City total more than six inches 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, Rhode Island, 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 Governor 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. (Reporting by Carey Gillam, additional reporting by Steve Barnes in Little Rock, Arkansas, and Scott Malone in Boston; editing by G Crosse and Gunna Dickson)