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, stranding thousands of holiday travelers. Authorities at times shut down major highways in parts of six 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 was closed to flights at mid-afternoon, and more than 1,000 were canceled through Thursday.

The runways will remain closed until at least Thursday night, spokesman Steve Snyder said. As many as 3,000 passengers were waiting for flights.

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.

The airport planned to set up hundreds of cots, although officials urged passengers to return home or check into hotels because its emergency supplies were limited.

"It's gotten progressively more hectic," airport spokesman Chuck Cannon said.

Colorado Gov. Bill Owens declared a state of emergency and activated the National Guard to rescue motorists.

Authorities closed portions of interstate highways in Wyoming, Nebraska, Colorado, Kansas, New Mexico and Texas throughout the day, including nearly all of Interstate 25 in Colorado, the state's busiest north-south route.

"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 postponed their game Wednesday night against the Phoenix Suns.

Travelers stalled by the closures poured into motels in Kansas and Nebraska.

"If you're westbound on the interstate, you can't get any further," said Sam Gill, who works at a Super 8 Motel in Ogallala, Neb. "I'm sure all the motels will fill up tonight."

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.

Back in Denver, some people — including the mayor — were trying to see the storm through a silver lining.

Mayor John Hickenlooper asked a staff member to contact a retailer that might be willing to donate sleds. He hoped to sponsor sledding at four parks around the city Thursday, serving hot cocoa and offering sleds to anyone without one.

"We can't do any more than what we're doing on the streets," he said. "But for a few hundred dollars, not a lot of resources, I think we can let people have a chuckle."