Commercial airlines around the world cancelled more than 4,300 flights over the Christmas weekend, as a mounting wave of COVID-19 infections driven by the Omicron variant created greater uncertainty for holiday travellers.
Nearly 10,000 more flights were delayed.
The website FlightAware showed 2,314 flights had been cancelled worldwide on Christmas Eve, a typically robust day in passenger transit. About a quarter of those suspended itineraries were in the United States.
Another 1,404 flights scheduled for Christmas Day were cancelled globally, the website said, along with 340 more that had been scheduled for Sunday.
The new coronavirus (or SARS-CoV-2) variant, known as Omicron (or B.1.1.529), was first identified by scientists in South Africa on November 24.
Omicron has already been detected in 106 countries, the WHO has said.
While recent research suggests Omicron produces milder illness, and a lower rate of hospitalisations, than previous variants of Covid-19, health officials have maintained a cautious note about the outlook.