More than 900 flights cancelled in U.S. as COVID-19 sidelines staff Christmas Day

U.S. airlines dropped over 900 flights Saturday, the second straight day of massive cancellations as surging COVID-19 infections sidelined some pilots and other crew, upending plans for tens of thousands of holiday travellers.

A total of 937 Christmas Day flights, including domestic ones and those into or out of the country, were cancelled, a rise from 690 on Christmas Eve, according to a running tally on flight-tracking website FlightAware.com. Nearly 1,500 flights were delayed.

The holidays are typically a peak time for air travel, but the rapid spread of the highly transmissible Omicron variant has led to a sharp increase in COVID-19 infections, forcing airlines to cancel flights as pilots and crew need to be quarantined.

United Airlines cancelled 230 flights, while American Airlines called off 90 mainline flights, representatives for the companies said in separate statements.

"The nationwide spike in Omicron cases this week has had a direct impact on our flight crews and the people who run our operation," United spokesperson Maddie King said. She said the cancellations made up a small portion of United's 4,000 average daily flights during the holiday season.

"We are working hard to rebook as many people as possible and get them on their way for the holidays," King said.

Winter weather and Omicron forced Delta Air Lines to scrub 344 mainline and connection flights on Saturday, of its approximately 3,000 scheduled flights, "after exhausting all options and resources to prevent those cancellations," a company spokesperson said.

"Delta expects more than 300 of its flights will be cancelled on Sunday, Dec. 26," the spokesperson said. "Delta people are working together around the clock to reroute and substitute aircraft and crews to get customers where they need to be as quickly and safely as possible."

Globally, FlightAware data showed nearly 2,650 flights were called off on Saturday and 6,233 others were delayed as of 3.27 p.m. ET.

Among the most impacted U.S. airports were Atlanta's Hartford-Jackson International, New Jersey's Newark Liberty International, Los Angeles International and New York's JFK International.

Not all airlines were affected equally. A spokesperson for Southwest Airlines said there were no issues to report on Saturday.

Omicron was first detected in November and now accounts for nearly three-quarters of U.S. cases and as many as 90 per cent in some areas, such as the Eastern Seaboard.

The average number of new U.S. coronavirus cases has risen 45 per cent to 179,000 per day over the past week, according to a Reuters tally.

While recent research suggests Omicron produces milder illness and a lower rate of hospitalizations than previous variants of COVID-19, health officials have maintained a cautious note about the outlook.

Ahead of Christmas, Americans scrambled for COVID-19 tests and many went ahead with their travel plans.

U.S. officials have said people who are fully vaccinated should feel comfortable proceeding with holiday travel.