Airlines have canceled thousands of flights in what has become a Christmas nightmare for so many as winter storms and staffing issues continue to wreak havoc across the United States.

Most major airlines have canceled or delayed thousands of flights, with Southwest Airlines canceling at least 70% of its flights on Monday due to a reported system crash. The airline also canceled 60% of its flights for Tuesday.

On Christmas Day, 42% of Southwest’s flights were canceled and 48% were delayed, according to data from FlightAware.

Southwest Airlines flight operations specialist James Davis said Monday evening that the nationwide “magnitude of the storm” affected all major airports.

“It’s just the fact that this one started in the west, swept east and hit almost every one of our biggest airports, which put us in a position where we struggled to recover. , and we struggled to get our flight crews and planes where they needed to be,” Davis said from William P. Hobby Airport in Houston.

Captain Casey Murray, president of the Southwest Airlines Pilots Association, said in a statement Monday that the ordeal had “been a disaster.”

“It’s been a failure on every level at Southwest. Our pilots, our front-line people have worked under tremendous stress trying to get our passengers from A to B, but we’ve had a rough ride when it comes to Southwest, Murray said, in part, adding that their ‘processes’, information technology or infrastructure ‘just weren’t there to support the operation.’

“And, unfortunately, our customers bear the brunt of that,” Murray added.

Angry Southwest customers took to Twitter on Monday, sharing their frustrations over delays, cancellations and long waits to speak to customer service agents.

“With consecutive days of extreme winter conditions on our network behind us, the continued challenges are having a significant impact on our customers and employees that is unacceptable,” Southwest said in a statement posted online. “And our sincere apologies for that are just beginning.”

Southwest said it was working to “respond to large-scale disruptions” by repositioning its crew and planes, which were all in the wrong place.

ABC News spoke to three stranded travelers – one staying overnight at a Boston airport until his new flight, one stranded in Chicago after his flight was canceled and one driving with a stranger to his cruise Disney in Tampa after flight problems.

Each traveler blamed the delays on the staff rather than the weather.

ABC News has reached out to American Airlines, JetBlue, Delta and United to learn more about the impact of staffing on their current delays and cancellations.

“I wanted to go home for Christmas,” Laetitia Duler, who was returning to San Francisco from Boston for the holidays, told ABC News. “As soon as I entered the queue, they said, ‘Your flights have been cancelled. Goodbye.””

Eric Jernigan was trying to fly from Jackson, Mississippi, to Tampa, Florida, for a Disney cruise when his Delta flight was canceled due to a lack of crew, he told ABC News.

He and five other people decided to fly to Florida after getting stranded at Jackson-Medgar Wiley Evers International Airport.

The city of Buffalo, New York, issued a travel ban as blizzard conditions moved through the area.

According to New York Governor Kathy Hochul and local officials, 29 people died in the state as a result of a massive lake-effect snowstorm.

Buffalo Niagara International Airport announced on Monday that it will be closed until Wednesday as its crews work “around the clock” to get the airport back into service.

ABC News’ Cherise Rudy contributed to this report.