Airlines canceled more than 2,800 flights on Monday, according to FlightAware.
More than 1,100 of the canceled flights were set to depart from or arrive in the US.
Some airlines attributed the cancellations to rising staff cases of COVID-19 and harsh weather.
After thousands of cancellations over the holiday weekend, airlines continued to slash flights on Monday amid rising cases of the Omicron coronavirus variant and bad winter weather.
As of Monday afternoon, 2,831 flights set to depart had been canceled, according to figures from the flight-tracking website FlightAware.
Of these cancellations, 1,148 were flights within, into, or out of the US, according to FlightAware data.
American Airlines canceled 86 flights, or 3% of its total flights for the day, and United Airlines canceled 95 flights, or 4% of its flights, according to FlightAware data.
Alaska Airlines canceled 144 flights scheduled for Monday, or 21% of its flights, and JetBlue canceled 66 flights, or 6% of its schedule.
Delta canceled 88 flights, Spirit canceled 71, and Horizon canceled 39.
And SkyWest, which is contracted for some regional flights by Alaska, American, Delta, and United, canceled 307 flights on Monday, or about 12% of its scheduled flights.
The bulk of Monday's canceled flights were operated by Chinese airlines, including China Eastern, which canceled 423 flights, and Air China, which canceled 198 flights. Elsewhere, the Indonesian airline Lion Air canceled 113 flights.
Monday's travel chaos came after airlines canceled about 3,300 flights on Sunday, with almost half of these departing from or arriving in the US, according to FlightAware data.
A Delta spokesperson said that the airline had canceled 748 flights between Friday and Sunday, including 161 of its 4,155 mainline and connection flights scheduled for Sunday and that staff were working to reroute and substitute aircraft and crews to get customers where they needed to be "as quickly and safely as possible."
Hong Kong has suspended some flights by Korean Air, Cathay Pacific, Emirates, and Qatar Airways from locations including London, New York, and Dubai, United Arab Emirates. Hong Kong said on Saturday that some arrivals had tested positive for the virus.
Omicron has caused a wave of sickness among airline staff
Some US airlines have attributed their cancellations to staff members who have caught or been exposed to the coronavirus.
An American Airlines spokesperson directed Insider to a statement from Saturday, which said the airline had precanceled some flights because of "a number of COVID-related sick calls" and notified passengers the day before. A SkyWest spokesperson said cases of the coronavirus among staff had risen, and the Delta spokesperson said the Omicron variant had impacted its schedule.
A United spokesperson told The Associated Press that Omicron's influence on staffing was unexpected and that it was unclear when operations would return to normal. Coronavirus cases among the airline's pilots are on the rise, United's senior vice president of flight operations said Sunday in a staff memo obtained by CNBC.
A JetBlue spokesperson told Fox Business that there was an "increasing number of sick calls from Omicron" and that the airline was trying to cancel flights that would cause the least disruption to passengers, and a SkyWest
Omicron is the dominant coronavirus strain in the US, and cases are surging in other countries, too. Studies suggest that the variant is more transmissible than previous variants, like Delta, and some data indicates that its symptoms are milder.
Delta, Alaska, and SkyWest spokespeople told Insider that harsh weather conditions, including heavy snow in Washington state on Sunday, were also to blame for some of the cancellations.
The Alaska spokesperson said that "severe winter weather" in the Pacific North West was having a "significant impact" on its operations, leading to the cancelation of 248 mainline flights that were scheduled to arrive or depart Seattle on Sunday. "Crew-related cancellations due to COVID are no longer a factor," the spokesperson said.
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