By late Saturday afternoon on the East Coast, more than 2,600 US flights and nearly 4,600 worldwide had been cancelled, according to tracking service FlightAware.

That is the highest single-day US toll yet since just before Christmas, when airlines blamed COVID-19 for increasing staffing shortages. More than 12,000 US flights have been cancelled since Decemeber 24.

The disruptions weren't just due to the virus, however. Wintry weather made Chicago, where 23 centimetres of snow was forecast, the worst place in the country for travellers. More than 800 flights were scrubbed at O'Hare Airport and more than 250 at Midway Airport.

Southwest cancelled more than 450 flights nationwide, or 13 per cent of its schedule. 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 blamed weather in Chicago, Denver and Detroit and COVID-19 illnesses.

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.

Sunday, when many travellers plan to return home from holiday trips, is shaping up to be difficult, too. A winter storm with heavy snow is expected to march toward the northeast as a new storm hits the Pacific northwest, according to the National Weather Service.

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 to Tuesday, said a union spokeswoman.

Airlines hope that extra pay and reduced schedules get them through the holiday crush and into the heart of January, when travel demand usually drops off. The seasonal decline could be sharper than normal this year because most business travellers are still grounded.

Travellers who stuck to the roads instead of the skies faced challenges, too. Transportation officials in the Midwest warned motorists that a mix of rain and snow could make roads slippery and reduce visibility, leading to hazardous driving conditions.

Australian Associated Press