An American Airlines Boeing 737 MAX airplane takes off on a test flight from Dallas-Fort Worth International Airport in Dallas, Texas, the US on December 2. Photo: VCG

US airlines scrapped nearly 1,000 flights on Saturday, the second straight day of massive cancellations as surging COVID-19 infections have sidelined some pilots and other crew members, upending plans for tens of thousands of holiday travelers over the Christmas weekend.

A total of 957 Christmas Day flights, including domestic flights and those into or out of the country, were canceled, up from 690 on Christmas Eve, according to a running tally on flight-tracking website FlightAware.com. Nearly 2,000 flights were delayed.

At least one airline said that it expects hundreds more cancellations on Sunday.

The Christmas 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 canceled 230 flights while American Airlines called off 90 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," she said.

Winter weather and Omicron forced Delta Air Lines to scrub 344 flights on Saturday, of approximately 3,000 scheduled flights, "after exhausting all options and resources to prevent those cancellations," a spokesperson for the company said, adding that the impact was likely to persist on Sunday.

"Delta expects more than 300 of its flights will be canceled on Sunday," 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 that just over 2,700 flights were called off on Saturday and another 7,049 were delayed, as of 5:30 pm EST.

Not all airlines were affected equally. A spokesperson for Southwest Airlines said there were no issues to report with the carrier's flights on Saturday.

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