Tens of thousands of travellers in the US were having their holiday plans upended by the Omicron coronavirus variant.

Airlines cancelled hundreds more flights on Sunday, citing staffing problems tied to Covid-19, as the nation’s travel woes extended beyond Christmas, with no clear indication when normal schedules would resume.

More than 700 flights entering, leaving or flying within the US were called off, according to the flight-tracking website FlightAware.

That figure was down from nearly 1,000 on Saturday, while more than 50 flights were already cancelled for Monday.

Delta, United and JetBlue have blamed Omicron for staffing shortages that forced cancellations.

“This was unexpected,” United spokesperson Maddie King said of Omicron’s impact on staffing.

Globally, airlines scrapped about 2,200 flights as of Sunday morning, down from more than 2,800 from the day before, FlightAware’s data showed. The site does not say why flights are cancelled.

JetBlue scrapped 10% of its flights on Sunday. Delta cancelled 5% and United cancelled 4%, according to FlightAware.

The three airlines cancelled more than 10% of their scheduled flights on Saturday.

American Airlines spokesman Derek Walls said the Christmas cancellations stemmed from virus-related sick calls.