New York, Dec 29 (IANS): Airlines continue to cut flights as rising numbers of staff are infected by the Omicron coronavirus variant and bad winter weather disrupts parts of the US.

As of Tuesday morning, 2,182 flights set to depart in the day have been canceled, and the cancellations have amounted to about 13,000 since Friday morning, according to figures from the flight-tracking website FlightAware.

Of Tuesday's cancellations, 675 -- just under a third -- were flights within, into, or out of the US. United Airlines has canceled 115 flights or 5 per cent of its total flights for the day. Alaska Airlines has canceled 50 flights scheduled for Tuesday or 8 per cent of its flights, and JetBlue has canceled 75 flights or 7 per cent of its schedule, according to the website's data.

"The highly contagious Omicron variant of Covid-19 has fueled a rising wave of infections across the US and caused significant disruptions to holiday travel," reported CBS News, noting that from Friday to Monday, more than 5,400 flights in the country were canceled and thousands more were delayed, with airlines citing staff shortages caused by Covid-19 infections among pilots, crew and other airline workers out sick.

Meanwhile, Delta, Alaska, and SkyWest said that harsh weather conditions in parts of the US, including heavy snow in Washington state on Sunday, were also to blame for some cancellations, reported Business Insider.

Delta has canceled 81 flights on Tuesday or 3 per cent, and Spirit has canceled 69 or 8 per cent. SkyWest has canceled 139 flights on Tuesday, or about 6 per cent of its scheduled flights.

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

Delta also said the cancellations are due to multiple issues, including the Omicron variant.

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

Airlines were already having trouble finding enough crew to meet the surge in demand for travel, said the report.

"Omicron is making that labor shortage even worse. Staffing shortages are leading to overworked flight crews and most of the canceled flights. Less choice in flights has led to higher ticket prices. And altercations over masks have been the cherry on the top of a miserable year for travel," it added.

Officials with various airline unions said that their members are stressed to the "breaking point" by work conditions because of understaffing. Many pilots and flight attendants said they're having trouble getting the hotel rooms they need to meet the government-mandated rest requirements while working, according to the report.

American Airlines and Southwest blamed service meltdowns in October and November on lacking enough pilots and flight attendants to adjust for weather-related cancellations. Pilots at American Airlines have held informational pickets in recent weeks to complain about work conditions, and the airline unions correctly predicted that the problems would get worse with the pick-up in travel over the holidays, it added.

Anthony Fauci, the nation's top infectious-disease expert, told MSNBC on Monday that "when you make vaccination a requirement, that's another incentive to get more people vaccinated. If you want to do that with domestic flights, I think that's something that seriously should be considered."

"Omicron is different ... It has extraordinary capability of transmitting very efficiently from person to person," he said.

The US already requires foreign visitors to show proof of vaccination to board an international flight to the country but there is no such rule for domestic travelers.

However, in a CNN interview on Monday evening, Fauci said that he doubted the US administration would call for vaccine mandates for domestic flights "in the reasonable foreseeable future."

US President Joe Biden, speaking to reporters on Monday, declined to say whether he endorsed a vaccine mandate for domestic air travel. The President has previously said he did not consider them necessary.