Major U.S. airlines canceled hundreds of flights Monday, the third consecutive day of widespread cancellations and delays over the Christmas weekend, as personnel and crew called in sick because of the Omicron spike.

As of 3 p.m. Monday, flight tracking FlightAware reported that more than 1,100 flights had been canceled in the United States.

There were almost 6,000 cancellations worldwide. Delta and JetBlue both had more than 100 cancellations. It is unclear whether the issues will be resolved entirely following the holiday travel rush.

According to FlightAware, Skywest canceled 297 total flights, accounting for 13% of its total flights. SkyWest said that coronavirus infections are causing its staff to be unavailable, but did not specify how long the issues could linger.

Airlines have been experiencing operational difficulties as millions of passengers from around the world continue to fly despite mounting coronavirus infections. The Transportation Security Administration reported Thursday that it checked 2.2 million people at airports around the country, the biggest number since the holiday travel season began a week ago.

SkyWest apologized for the disruption and said it was working to return normal operations as soon as possible.

Other carriers that have been struck severely include Alaska Airlines, which has 141 cancellations, American Airlines, which has 86, United, which has 94, and Delta, which has 81.

Delta, which was one of the airlines hardest impacted by cancellations over the weekend, told FOX Business that it may be seeing an improvement in cancellations compared to the 375 flights it canceled on Christmas Day.

FlightAware said United canceled 201 flights on Friday, accounting for 10% of its overall schedule, and 238 flights on Saturday, accounting for 13% of its total schedule.

In addition, on the day before Christmas, JetBlue canceled 80 flights, or nearly 7% of its total schedule.

Alaska Airlines issued a statement saying that 17 flights were canceled on Thursday because of the virus. On Friday, the airline canceled 11 flights.

Meanwhile, the Chinese Consulate in San Francisco protested Monday when Delta Air Lines blamed new pandemic-related disinfecting standards at a Shanghai airport for the cancellation of a recent Seattle-to-Shanghai flight.

The new directives at Shanghai Pudong International Airport, according to an emailed statement, demand significantly prolonged ground time and are "not operationally sustainable for Delta."

In the midst of a developing epidemic in Xi'an and six weeks before the Winter Olympics in Beijing, China is tightening its already rigorous COVID-19 travel requirements, making it more difficult for foreigners to visit the country.