New York, New York - Thousands of flights were canceled in the US and around the world over the Christmas holidays as the highly infectious Omicron variant wreaked havoc on airlines.

On Saturday, more than 2,300 commercial flights were canceled, around 800 of them in the US, according to the FlightAware tracking website. A similar number of flights were axed on Friday.

Airlines had been hit by a shortage of healthy staff amid a spike in Covid-19 infections fuelled by the now-dominant Omicron strain.

A spokesperson for Delta Air Lines told the New York Times that "a combination of issues, including weather and Omicron-related issues," were to blame.

United Airlines cited crew illnesses as the main cause of flight disruptions.

German carrier Lufthansa announced on the Thursday before Christmas that it would have to cancel a dozen long-haul flights between December 23 and 26 because so many pilots had called in sick.

A spokesperson told DPA on Saturday that the number of canceled flights had not increased.

In addition to a connection to Tokyo, the affected Lufthansa flights are mainly to and from US destinations.

The German carrier said it would not speculate on what role Omicron played, as it was not informed about the nature of the employee illnesses.

FlightAware also showed hundreds of canceled flights worldwide for Sunday.