NEW YORK (BLOOMBERG) - More than 2,600 flights into and out of the US were cancelled on Saturday (Jan 1), and more than 4,000 were delayed, according to the tracking firm FlightAware.com, amid bad weather and staff shortages caused by the rapid spread of the Omicron variant.

Southwest Airlines cancelled 472 flights and delayed another 798 – a third of all its scheduled trips; while regional carrier SkyWest Inc cancelled 479 flights and delayed another 406, more than 44 per cent of all its scheduled flights.  

Among the bigger national carriers, Delta Air Lines Inc cut 10 per cent of its flights while American Airlines Group Inc and United Airlines Holdings Inc each scrubbed 7 per cent, according to the site.

Some 1,050 flights into or out of the US have already been cancelled for Sunday and 202 scrubbed for Monday, FlightAware said.

A heavy snow storm across large parts of the country is expected to cause major travel disruptions, according to the National Weather Service.

With the US hitting record Covid-19 infections, the holiday travel season has been snarled by about 12,000 cancelled flights since Christmas Eve, according to the Associated Press.

Some of the biggest troublespots for travellers were in the Midwest, where where 55 per cent of flights scheduled to leave from Chicago Midway and 45 per cent from Chicago O'Hare were scratched, according to FlightAware.

Airports in Denver, Kansas City and Detroit also saw a high number of cancellations and delays.

The Transportation Security Administration, which has been grappling with unruly passengers, urged people to "be patient."

Security screened more than 1.6 million people yesterday at checkpoints around the country.