Airports around the U.S. struggled Friday to cope with a rising flood of frustrated Christmas travelers stranded when thousands of flights were canceled by a near-record two-day blizzard that paralyzed Denver.

Flights resumed at Denver International Airport midday Friday, though thousands remained stranded or stuck.

United Airlines spokesman Jeff Kovick said it could be days before some people are able to get on a flight. The 2,000-plus canceled flights at Denver, the nation's fifth-busiest airport, caused a ripple effect that disrupted air travel around the country just as the holiday crush began.

"We're asking for their patience as we work to get people where they need to be as soon as we safely can," Kovick said.

Frontier spokesman Joe Hodas said the airline has 65,000 bumped passengers to move systemwide and the airline was already 90 percent booked for the holidays. "Do the math," he said.

Click here to see FOXNews.com's Colorado snowstorm photo essay

Many of the travelers stranded by the storm are stuck waiting on standby, though, hoping to get on another flight at a time when airlines rarely have open seats.

Atlanta businessman Scott Carr, standing in the Frontier Airlines line that wrapped around to the opposite side of the terminal, said he had booked four flights on three different airlines to increase his chances of making it home for Christmas and was considering driving to Kansas City to catch a flight.

"If I have to drive, at least I'll be getting closer," he said.

Frontier spokesman Joe Hodas said the airline has 65,000 bumped passengers to move systemwide and the airline was already 90 percent booked for the holidays.

An estimated 4,700 travelers spent Wednesday night at the airport. By Thursday evening, about two-thirds of them had found hotel rooms, but others still slept on cots in the airport, in chairs or wrapped up in coats and makeshift cardboard shelters on the concourse floors.

Workers in orange vests directed the human traffic and offered blankets and what other supplies they could to the stranded travelers.

In other airports across the country, tens of thousands of travelers have been rerouted and stranded, complicating the pre-Christmas travel crunch.

The storm, Colorado's worst since a March 2003 blizzard, brought life to a standstill for 3.8 million people along the Front Range — a 170-mile urban corridor along the eastern edge of the Rockies that includes Denver.

Some mountain areas got more than 3 feet of snow, and up to 25 inches fell in the Denver metropolitan area. Bus and train service was shut down. Police and National Guard soldiers rescued hundreds of people stuck in cars.

In Wyoming, a woman died while walking for help after her car became stuck in the snow, officials said. In Kansas, a woman was hit by a tractor-trailer on an icy road.

Denver's normally bustling downtown began showing signs of life as the sun came out Thursday afternoon. Mail delivery across the region was still suspended, however, and many malls were closed on what should have been one of the busiest shopping days of the year.

The Associated Press contributed to this report