(CNN) -- Travel through the southern Rockies into the central Plains "will be dangerous, if not impossible" Tuesday, forecasters warned, as a winter weather system blasts broad swaths of the West and Midwest.
Blizzard warnings stretched from southeast Colorado through western Kansas, the Oklahoma panhandle and far northern Texas, according to the National Weather Service.
"Blizzard conditions with wind chill temperatures below zero are expected," the agency said.
Warnings that had threatened northeast New Mexico, however, had expired by late Tuesday morning.
Still, winter storm warnings stretched farther across that state, Colorado and into Kansas.
Heavy snowfall was reported in eastern Colorado and western Kansas on Tuesday, along with freezing rain and sleet across south-central Kansas. Blustery winds of 20 to 50 mph were also reported.
But "it appears the heaviest snowfall with this system has ended, as the disturbance tracks toward eastern Oklahoma," the National Weather Service said.
Snow across the Rockies was expected to end late Tuesday morning, but will continue across the central Plains until late in the day, the weather agency said.
But areas such as Pie Town, New Mexico, and La Junta and Springfield, Colorado, have already seen more than 15 inches of snowfall since Sunday evening.
Interstates and highways were shut down Monday night as at least five states contended with heavy snow, fierce winds and ice.
Visibility in parts of western Kansas and southeast Colorado was less than a quarter-mile, said Ariel Cohen, a meteorologist with the National Weather Service's Storm Prediction Center in Norman, Oklahoma.
New Mexico State Police shut down Interstate 40, a major east-west artery, from Albuquerque to the Texas state line, saying there was zero visibility because of blowing snow. Interstate 25 was shut down from just north of Albuquerque to the Colorado state line because of the blizzard conditions, which included snow-packed and icy roads.
The state police also shut down U.S. and state highways in the northeast corner of the state.
Texas authorities closed I-40 westbound in the Texas panhandle at New Mexico's request Tuesday morning but had reopened it by mid-afternoon.
"Our biggest concern is ice coming out of Amarillo," said Gabriel Medrano, a spokesman for the state's Department of Public Safety. "We had several calls for stranded motorists. We had troopers and National Guard assisting, pulling people from their vehicles."
Vehicle crashes were reported around Amarillo, which lies along I-40 in the Texas panhandle, he added.
Medrano said his office had received "dozens (of) calls for assistance," though most of them came from people "west out of Oldham County."
His agency and the Texas Department of Transportation said motel rooms had filled in Tucumcari, New Mexico, the first major town on I-40 across the state line, because drivers weren't allowed to travel any farther on the highway.
Meteorologists call the storm system a strong one that is producing "very hazardous" conditions. And while such storms typically occur around winter, the large area of strong winds combined with the snow is considered unusual.
Texas Gov. Rick Perry activated the Texas Military Forces as a precaution to provide help on the roads, his office said.
Snow accumulations of up to 6 inches were likely, with higher accumulations expected across the northwest Texas Panhandle, Perry's office added.
Flights were canceled at Rick Husband Amarillo International Airport for Tuesday morning, spokesman Patrick Rhodes said, but normal operations have since resumed.
To the north, in the Oklahoma panhandle, U.S. highways were closed and transportation workers were salting the roads, according to Michaelann Ootean of the Oklahoma Department of Emergency Management.
Roads and highways were "completely snow-packed" or covered with ice in much of western Kansas on Monday, according to the state's Department of Transportation. They included Interstate 70, which crosses the state from west to east, and Interstate 135 through Salina.
U.S. highways 50 and 54 were shut in southwest Kansas. The DOT said U.S. 50 was closed because of blizzard conditions and "multiple accidents" in Colorado.
The Colorado Department of Transportation shut down highways across the southeastern part of the state because of snow and icy conditions. Interstate 25 was shut southbound from Pueblo to the New Mexico state line, and the DOT said lodging was unavailable south of Colorado City. Northbound I-25 remained open.
CNN's Nick Valencia, Tracy Sabo and Greg Morrison contributed to this report.