A major snowstorm blew across Colorado toward the Plains on Wednesday, dumping more than a foot of snow in some places and forcing the airport to close, grounding hundreds of flights full of holiday travelers. Authorities shut down major highways in parts of four states.

The National Weather Service posted blizzard warnings for most of eastern Colorado and adjoining sections of Nebraska and Kansas. A day earlier, the storm had pummeled New Mexico with up to a foot of snow.

As much as 20 inches of snow was forecast in Denver, where all nonessential municipal offices were closed early. Snow was predicted to fall through Thursday morning.

The storm struck Denver just as the morning commute was starting.

"I'm going to grab my computer, talk to my boss and go back home," Jennifer Robinson said after driving about 20 miles from her home in Boulder to her sales job in downtown Denver. "I'm not going to take a risk and get stuck in Denver."

Denver International Airport closed in mid-afternoon. More than 1,000 flights were canceled through Thursday.

Stranded travelers sprawled on benches and floors, or stood in long lines at ticket counters trying to make new reservations.

"I'm trying to book another flight, but I'll probably be spending the night at the airport," said Michael Heitc, 54, of Denver, who was trying to get to Oregon to visit relatives for the holidays.

Colorado Gov. Bill Owens declared a state of emergency and activated the National Guard in case stranded motorists needed to be rescued.

Police closed I-70 for more than 250 miles from just east of Denver to WaKeeney, Kan., and sections of I-80 along a 140-mile stretch from Cheyenne, Wyo., to Big Springs, Neb., because of visibility near zero and slippery pavement. I-25, Colorado's busiest north-south route, was from Wyoming to New Mexico, almost 300 miles; only about 35 miles in the Denver area were open. The entire length of I-76, from Denver to near the Nebraska border, was closed.

"They pulled everyone off the highway," said Leon Medina, manager of a truck stop on Interstate 25 in Walsenburg, about 130 miles south of Denver. "Cars are all around the building. Trucks are all over, trucks and cars pulled into ditches."

Scores of schools were closed, and the NBA's Denver Nuggets canceled their game Wednesday night against the Phoenix Suns.

Travelers stalled by the closures filled Kansas motels, said Stan Whitley, a spokesman for the state Department of Transportation.

The lumbering storm dropped more than a foot of snow in Colorado's southwestern mountains Tuesday, with 19 inches at the Wolf Creek ski area and 17 at Durango Mountain Resort.

"We've been waiting for a big storm to hit, so this was the best early Christmas present," Durango Mountain Resort spokeswoman Loryn Kasten said.

Winter storm or blizzard warnings were in effect for much of Nebraska, with up to 12 inches of snow expected by Thursday morning. Rain spread across much of the rest of the Plains.

Roads around New Mexico were still snowpacked and icy Wednesday. Numerous schools opened late or remained closed. Los Alamos National Laboratory was closed for the day.

Up to a foot of snow fell at higher elevations of northwest and west-central New Mexico on Tuesday, and snow and sleet closed sections of I-40 for a time across eastern New Mexico and in the Texas Panhandle. Albuquerque International Airport was closed for several hours Tuesday as snow covered runways.

In Denver, Chris and Erica Govea couldn't figure out what the fuss was about. The Fresno, Calif., couple were in town to celebrate their 10th wedding anniversary, and had picked the city after seeing it on televised Denver Broncos games.

Strolling through the snow, bundled in puffy coats and laden with shopping bags, Chris Govea said, "We thought it was always like this."