Some 7,500 flights were previously cancelled by airlines worldwide over the Christmas weekend.
Air travel has continued to be severely disrupted in the United States, with bad weather in parts of the country adding to the impact of a massive spike in Covid-19 infections fuelled by the Omicron variant.
The United States has 2,723 cancelled flights, more than half of the 4,698 cancelled worldwide, till around 11:00 pm (0400 GMT) on Sunday, according to tracking website FlightAware.
In addition, 5,993 domestic flights were delayed on Saturday, out of a total of 11.043 worldwide for the day.
The worst affected US airline was SkyWest, which had to cancel 23 percent of its flight schedule, according to the site.
READ MORE: Christmas weekend sees thousands of flights cancelled globally
Chicago airports hard-hit
In the United States, airports in Chicago were particularly hard-hit because of bad weather, with a snowstorm expected in the area on Saturday afternoon and into the night.
The global air travel industry is still reeling from the highly contagious Omicron variant.
Many pilots, flight attendants and other staff are absent from work after contracting Covid-19, or because they are quarantining after coming in contact with someone who has the infection.
READ MORE: Experts warn of 'viral blizzard' as Omicron rages in US
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