Airlines continued to scrub flights on Friday as COVID-19 infections hit pilots and flight attendants, leaving carriers short-staffed to operate busy schedules over the Christmas holiday weekend.

Airlines have canceled more than 600 U.S. flights so far on Friday, calling off hundreds more scheduled for Saturday, in the latest sign of how the rapidly spreading Omicron variant is upending business even in industries with heavily vaccinated workforces, said The Wall Street Journal on Friday.

Cancellations in the United States climbed at carriers including United Airlines and Delta Air Lines, which have rushed to reassign and reroute pilots and planes to cover the flying, even offering additional pay to encourage healthy employees to pick up shifts over the Christmas holiday.

United canceled over 185 mainline flights, 10 percent of what was scheduled on Friday, and another 120 on Saturday, according to FlightAware, a flight-tracking site. Delta canceled about 160 of some 3,100 flights planned for Friday and expects upward of 150 cancellations on Saturday and Sunday.

"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 as safely as possible," the airline said in a statement.

"The Omicron variant is becoming an increasingly disruptive force as it tears around the world. Its accelerating spread hampered operations and slowed sales at some businesses over the course of just a few days," said the report.