On Sunday, more than 2,000 flights were cancelled – over 640 of which were to or from US airports, according to FlightAware.
The worst-hit US companies are Delta, United and JetBlue.
United warned earlier that a spike in 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.
Omicron now is the dominant strain in the US.
However, the most affected single airline appears to be China Eastern with more than 390 scrapped flights on Sunday.
The airport in the northern Chinese city of Xi’an has reported more than 100 flight cancellations.
Heathrow Airport in London has seen 60 flights cancelled on Sunday so far.
Nearly 5.4 million people have died with coronavirus worldwide, according to America’s Johns Hopkins University. There have been more than 279 million confirmed cases.