More than 3,000 flights were cancelled around the world on Sunday, more than half of them US flights, adding to the toll of holiday week travel disruptions due to adverse weather and the surge in coronavirus cases caused by the Omicron variant.

Over 3,300 flights had been cancelled by noon GMT on Sunday, including over 1,900 entering, departing from or within the US, according to a running tally on the tracking website Including those delayed but not cancelled, more than 4,800 flights were delayed in total.

Covid-19: Flight cancellations ruin holiday plans for thousands

The Christmas and New Year holidays are typically a peak time for air travel, but the rapid spread of the highly transmissible Omicron variant has led to a sharp increase in Covid-19 infections, forcing airlines to cancel flights as pilots and crew quarantine.

Transportation agencies across the US were also suspending or reducing services due to coronavirus-related staff shortages.

Rising Omicron numbers

Omicron has brought record case counts and dampened New Year festivities around much of the world.

Why Covid-19 means the era of ever cheaper air travel could be over

The rise in US Covid-19 cases had caused some companies to change plans to increase the number of employees working from their offices from Monday.

Chevron Corp was to start a full return to office from January 3 but told employees in late December it was postponing the move indefinitely.

US authorities registered at least 3,46,869 new coronavirus infections on Saturday, according to a Reuters tally. The US death toll from Covid-19 rose by at least 377 to 8,28,562.

US airline cabin crew, pilots and support staff were reluctant to work overtime during the holiday travel season, despite offers of hefty financial incentives. Many workers feared contracting Covid and did not welcome the prospect of dealing with unruly passengers, some airline unions said.

In the months preceding the holidays, airlines were wooing employees to ensure solid staffing, after furloughing or laying off thousands over the last 18 months as the pandemic hobbled the industry.