Chicago, Feb 02(Agencies): A monster winter storm in United States stretching from New Mexico to Maine laid down a sheet of ice on the Plains and lower Midwest on Tuesday, turning to snow as it tiptoed north, and forecasters said the worst was yet to come.

"We're looking at heavy snow from the Rockies to New England," said Pat Slattery, National Weather Service spokesman.

The storm was expected to affect as much as a third of the U.S. population, from severe thunderstorms in the Southeast and ice-coated roads in Texas to blizzard conditions and up to 2 feet of snow in Chicago. Several regions were experiencing bitter cold, including Denver, where mid-afternoon readings fell to six degrees below zero.

About 200 National Guard troops were called out to assist local law enforcement in the St. Louis area.

Major U.S. airlines said they had canceled more than 5,400 flights ahead of the storm. More than 1,200 of those flights were in and out of Chicago-area airports, major airline hubs.

One of the hardest-hit cities on Tuesday was Kansas City, where a municipal state of emergency was declared and snow plows were pulled from runways at the international airport in late afternoon due to blowing snow and low visibility.

Statewide emergencies were declared in Missouri, Oklahoma, Illinois and Wisconsin. White-out conditions were reported on Interstate 44 between Oklahoma and Missouri, closing part of that highway, as well as Interstate 70 in central Missouri.

Storm-related outages knocked out power to more than 100,000 homes and businesses in at least eight states, including Texas, Louisiana, Arkansas, Missouri, Kentucky, Indiana, Illinois and Ohio.