More than 1,500 flights have been canceled in the run-up to Christmas, leaving holidaymakers stuck far from loved ones.

According to data from flight-tracking site FlightAware, the rise in Omicron cases across the globe is primarily to blame, with United Airlines canceling at least 150 Christmas Eve flights in the US.

"The nationwide spike in Omicron cases this week has had a direct impact on our flight crews and the people who run our operation," wrote a United employee memo viewed by CNN.

The airline stated in a message to customers: "We're sorry for the disruption and are working hard to rebook as many people as possible and get them on their way for the holidays."

And the mayhem could continue into Christmas Day.

A United spokeswoman told The New York Times: "We are really managing this day by day. There may be even additional flight cancellations for Saturday. It's possible."

Also, in the US, Delta has scrapped more than 100 Christmas Eve flights at the last minute.

The carrier ascribed the cancellations to numerous circumstances, including the Omicron surge.

"We apologise to our customers for the delay in their holiday travel plans," Delta added.

"Delta people are working hard to get them to where they need to be as quickly and as safely as possible on the next available flight."

Alaska Airlines has also canceled 17 flights and stated further cancellations may happen today due to the Omicron variant.

Elsewhere, Australia has witnessed repeated flight cancellations in Sydney and Melbourne amid high numbers of coronavirus infections.

Some 80 services out of 500 scheduled to arrive at or depart from Sydney on 24 December have been canceled; more than 10 percent of Melbourne's Christmas Eve flights are off (more than 70 out of 700). (more than 70 out of 700). Brisbane Airport has canceled 45 flights so far.

"A large number of our frontline team members are being required to test and isolate as close contacts given the increasing number of cases in the general community," a Jetstar Airways representative said of the disruption to services.

"As a result, we have had to make some late adjustments to our schedule."

Closer to home, Ryanair has reduced its January schedule by a third due to new European travel restrictions designed to stem the spread of Omicron.

Europe's biggest budget carrier said the stricter border controls had "notably weakened" near-term Christmas and new year bookings and that January capacity was reduced from a planned 10 million passengers to six-seven million.