Passengers line up at John F. Kennedy International Airport after airlines announced numerous flights were canceled on Christmas Eve in Queens, New York City, US, December 24, 2021. ( Photo by REUTERS)

Millions of people have faced travel disruption over Christmas after airline companies have cancelled thousands of flights worldwide as the surging Omicron variant creates greater uncertainty and misery for holiday travelers.

A combination of issues, including weather, staffing shortages, COVID-19, and the omicron variant are blamed for cancellation of 4,500 flights across the world over Christmas Eve and Christmas Day.

More than 3,800 flights were cancelled worldwide on Christmas Day and only on Friday around 2,400 cancellations were reported, according to Flightaware.com. More than half of the cancellations came from Chinese airlines and about 20% were from US-based carriers.

Thousands of would-be travelers, looking forward to seeing family and friends for Christmas were informed at the last minute that their flights had been canceled and the main reason was that due to highly contagious omicron variant of coronavirus.

Also, pilots, flight attendants and other staff have been calling in sick or having to quarantine after exposure to COVID.

Staffing shortages have been affecting a range of service industries as the virus continues to spread.

The holiday cancellations are just the latest challenge for airline industries during one of the year’s peak travel periods. To accommodate the surge in Christmas travelers, some airlines had offered employees incentive pay to work extra hours or not call in sick.

Germany-based Lufthansa said Friday it was cancelling a dozen long-haul transatlantic flights over the Christmas holiday period because of a massive rise in sick leave among pilots.

Lufthansa, Delta, United Airlines faced the most flight cancellations.

Delta airline said it cancelled flights on Friday because of the impact of Omicron and possibility of bad weather after it had exhausted all options and resources - including rerouting and substitutions of aircraft and crews to cover scheduled flying.

It said in a statement to several news outlets that it was trying to get passengers to their destinations quickly.

Many European countries are preparing to impose restrictions just after the festive period, which will restrict private gatherings to 10 people or even less. Football matches will also be played behind closed doors in Europe in 2022.