A storm that began Wednesday and continued into Thursday afternoon dumped more than half a metre of snow on Colorado, bringing much of the state to a halt.

Schools, malls and offices were closed Thursday, the governor declared a state of emergency and 4,700 travellers spent the night at Denver International Airport after flights were cancelled.

A bicycle wasn't much use on Wednesday night in Denver.
(Bill Ross/Associated Press)

The Colorado National Guard was rescuing stranded drivers flooding into shelters.

Mail deliveries were cancelled in the eastern part of the state. Avalanche warnings were issued in the mountains.

An afternoon notice on the airport website said it would not open until Friday. Cleaning crews could not keep up with the drifting and falling snow, a spokesman said.

More than 1,000 flights were cancelled on Wednesday and Thursday morning.

The city is using buses to try to take stranded passengers to hotels from the airport, but those stranded had a hard night.

Mike Gelski, who manages a Domino's Pizza at the airport, said he slept on the floor with just a blanket.

Some people are getting cranky, but there's also a cameraderie, he said. "People are sharing what they got with other people, which is really cool."

The snow is forecast to stop Thursday afternoon, after adding up to five more centimetres, but winds have formed drifts and a major cleanup looms.

The U.S. National Weather Service had a blizzard warning in effect for part of eastern Colorado at 1 p.m. ET, but scaled back advisories for parts of adjacent states — western Nebraska, southern Wyoming and western Kansas — from the earlier blizzard warning.

Colorado Gov. Bill Owens said declaring an emergency and activating the  National Guard would help drivers. The guard also delivered supplies to the Denver airport.

Hundreds of kilometres of highways are closed. Accidents and stalled cars made the mess worse, though there were no traffic deaths, police reported.

About 210 kilometres from Denver in a truckstop in Walsenburg on Interstate 25, the main highway south from Denver, manager Leon Medina described the scene: "Cars are all around the building. Trucks are all over, trucks and cars pulled into ditches."

With files from the Associated Press