About 20 percent of the U.S. population -- roughly 60 million people in 20 states -- were under winter weather warnings, watches and advisories, CNN reported.
AccuWeather.com reported blizzard conditions in portions of northern Oklahoma, Kansas, Nebraska and Missouri Thursday.
Missouri Gov. Jay NIxon declared a state of emergency in the "Show-Me" state, which was bracing for at least 10 inches of snow. Kansas City, Mo., Mayor Sly James declared a state of emergency in the city, where CNN reported 250 snow plows were working to clear roads and the public was urged not to travel unless necessary.
Forecasters said nearly a foot of snow already piled up over some communities in Kansas. Kansas State University in Manhattan, Kan., canceled Thursday classes, CNN said.
The Oklahoma Department of Transportation said weather conditions Wednesday were to blame for the death of an Alex, Okla., high school senior, The (Chickasha) Express-Star reported. Officials said the teen died in a traffic collision involving a truck.
Travel was extremely dangerous along major interstates, including I-35, I-70 and I-80, AccuWeather.com said.
Kansas City International Airport in Missouri said some flights were canceled and urged passengers to check on their flight status before heading to the airport.
The Federal Aviation Administration said snow and ice were causing flight delays and cancellations at Denver International Airport as well.
Dozens of schools closed across the Plains states, CNN said.
Crews have been treating streets since Monday in Wichita, Kan., officials said.
Thousands of utility customers in Oklahoma were without power because of the storm, The (Oklahoma City) Oklahoman reported.
As of 6:45 a.m. CST Thursday, the Kansas Department of Transportation said most major highways across the state were snow- and ice-packed and travel was extremely dangerous.
The system eventually will stretch from Texas to the Dakotas, CNN reported, bringing snow to the north, torrential rains and tornadoes along the Gulf Coast and freezing rain over Arkansas and Missouri.
The storm is expected to provide some relief for agriculture in the Plains, Accuweather.com said.