FlightAware says more than 2,600 flights were cancelled in the US, nearly 4,600 worldwide.
Air travel continues to be severely disrupted in the United States, with bad weather in parts of the country adding to the impact of a surge in COVID-19 infections fuelled by the Omicron variant.
The US had 2,604 cancelled flights on Saturday, more than half of the 4,529 cancelled worldwide, shortly after 4:30pm (21:30 GMT), according to tracking website FlightAware.
Among international carriers, China Eastern scrubbed more than 500 flights, or about one-fourth of its total, and Air China cancelled more than 200 flights, one-fifth of its schedule, according to FlightAware.
The US cancellations represent the highest single-day toll since just before Christmas when airlines began announcing staffing shortages as a result of increasing COVID infections among crews.
The worst-affected US airline was Southwest, which had to cancel 450 flights nationwide or 13 percent of its flight schedule, according to the site.
American Airlines and Delta Air Lines scrubbed more than 200 flights each, and United Airlines cancelled more than 150.
SkyWest, a regional carrier that operates flights under the names American Eagle, Delta Connection and United Express, grounded 480 flights, one-fourth of its schedule. A spokesperson said weather in the cities of Chicago, Denver and Detroit as well as a COVID spike were to blame.
Airports in Chicago were hit particularly hard because of difficult weather, with a snowstorm expected in the area on Saturday afternoon and into the night.
More than 800 flights were scrubbed at O’Hare Airport and more than 250 at Midway Airport.
More than 12,000 US flights have been cancelled since December 24.
Airlines say they are taking steps to reduce cancellations. United is offering to pay pilots triple or more of their usual wages for picking up open flights through most of January. Spirit Airlines reached a deal with the Association of Flight Attendants for double pay for cabin crews through Tuesday, said a union spokeswoman.
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, or are quarantined after coming into contact with an infected person.