Thousands of flights canceled on Christmas weekend

New York(CNN Business) Major US airlines canceled hundreds more flights Sunday, the third day in a row of mass cancellations and delays over Christmas weekend, as staff and crew call out sick amid the Omicron surge.

More than 1,200 US flights were canceled and more than 5,000 were delayed Sunday, according to FlightAware. Globally, there were over 2,000 cancellations. Delta and JetBlue each saw over 100 cancellations Sunday.

Globally, airlines canceled more than 6,000 flights on Christmas Eve, Christmas and the day after Christmas, according to FlightAware. That includes about 1,700 flights within, into or out of the United States.

Operational snags at airlines are coming as millions are still flying in spite of rising coronavirus cases. The TSA says it screened 2.19 million passengers at airports across the country on Thursday, the highest figure since the uptick in holiday travel started a week ago.

More than a thousand US flights canceled

On Thursday, United Airlines (UAL) said it had to "cancel some flights" because of the Omicron variant of the coronavirus.

"The nationwide spike in Omicron cases this week has had a direct impact on our flight crews and the people who run our operation," said a United memo obtained by CNN.

United canceled 201 flights on Friday, representing 10% of its total schedule, and 238 flights on Saturday, representing 12% of its schedule, according to flight tracking site FlightAware.

United said it is "notifying impacted customers in advance of them coming to the airport," according to a company statement. "We're sorry for the disruption and are working hard to rebook as many people as possible and get them on their way for the holidays."

Later Thursday night, Delta Air Lines (DAL) also canceled flights. The airline canceled 173 Christmas Eve flights, according to FlightAware.

Delta said the cancellations are due to multiple issues including the Omicron variant.

"We apologize to our customers for the delay in their holiday travel plans," Delta said in a statement. "Delta people are working hard to get them to where they need to be as quickly and as safely as possible on the next available flight."

Additionally, JetBlue (JBLU) canceled 80 flights, or about 7% of its overall schedule, on the day before Christmas.

Alaska Airlines said in a statement that it canceled 17 flights because of Omicron on Thursday. The airline canceled 11 flights Friday.

International flights canceled

China Eastern canceled 960 flights on Saturday and Sunday, and Air China canceled 465, according to FlightAware.

Shenzhen Airlines, Lion Air and Wings Air canceled dozens of flights as well.

In Japan on Sunday, more than 100 domestic flights were grounded due to heavy snow in the northern and western parts of the country, according to Japan's two biggest airlines, ANA Holdings and Japan Airlines.