A quarter of the more than 4,000 flights cancelled worldwide on Friday and Saturday were in the US, according to website Flightaware.
The issue came amid crews testing positive, or being forced to self-isolate to stem the spread.
The US, like countries around the world, has seen a sharp rise in cases.
Despite early findings that Omicron is milder than other variants, scientists are concerned by the sheer number of infections.
“When we have millions and millions and millions of people, all sick, all together at one time, it doesn’t take a large percentage of those people to topple over the hospitals.
” Associate professor of internal medicine at the University of Michigan, Dr Hallie Prescott, told the New York Times.
In the UK – which once again saw record-breaking case numbers on Friday – volunteers are preparing for a Christmas Day ‘booster jabs’ push to reduce the impact of Omicron.
Across Europe, governments are bringing in their own measures to combat the increase:
Italy, Spain and Greece have made face masks compulsory outdoors again.
Catalonia, in north-eastern Spain, has imposed an overnight curfew.
The Netherlands entered a strict lockdown earlier this week.
Germany has said it will restrict private gatherings to 10 people and close nightclubs from 28 December.
Football matches will be played behind closed doors.
Portugal has ordered bars and nightclubs to shut from 26 December, and made working from home obligatory until 9 January.
But in South Africa – where the Omicron variant was first identified – the government has ended Covid contact tracing, except for serious cluster outbreaks or prisons.
The health department announced that as most of the population had now been exposed to the coronavirus, the policy is now shifting from a containment strategy to one of mitigation including self-monitoring, mask wearing and social distancing
The US earlier announced it would lift travel restrictions imposed on South Africa and seven other African countries because of concerns about the Omicron variant on 31 December.
Travellers from South Africa, Botswana, Zimbabwe, Namibia, Lesotho, Eswatini, Mozambique and Malawi had been blocked since 29 November.
America’s top infectious disease expert, Dr Anthony Fauci, warned earlier this week that Christmas travel would increase the spread of the variant even among the fully vaccinated.
However, thousands found their plans thrown into disarray as flights across the country were cancelled.
At 03:30 GMT Saturday, 689 flights into or out of the US have been cancelled on Friday, the FlightAware website reported, with more than 700 are expected to be cancelled on Christmas Day itself.
The worst affected US companies are Delta, United Airlines and American Airlines.
United Airlines said rising numbers of Omicron cases had “had a direct impact on our flight crews and the people who run our operation,” adding that it was contacting impacted passengers in advance of them coming to the airport.
Overall, global airlines have cancelled more 4,000 flights scheduled to take off on Friday and Saturday.
In Australia, thousands of festive journeys were affected on Friday with more than 100 domestic flights from Sydney and Melbourne to other cities cancelled.
A spokesperson for Jetstar, which accounted for many of the cancellations, said the airline had rebooked “the vast majority” of affected passengers “within a few hours of their original departure time so they can get to their destination in time for Christmas.
More than 5.
3 million people have died with coronavirus worldwide, according to America’s Johns Hopkins University.
There have been 279 million confirmed cases.
BBC /Shakirat Sadiq
Covid: US Airlines Scrap hundreds of Flights Amid Omicron Surge