Holiday travel headaches and safety worries swelled Sunday with thousands of flights cancelled, events scrapped and new Omicron cases soaring, as people wrap up Christmas celebrations bruised by a resurgent Covid pandemic.
Some 7,900 flights have been grounded and tens of thousands more delayed from Friday through Sunday -- one of the busiest travel periods of the year -- with multiple airlines acknowledging that Omicron spikes have prompted staffing shortages.
Effects have rippled worldwide, and the hurt was expected to bleed into the work week, with some 800 flights already facing cancellations Monday and 170 more on Tuesday, according to flight tracker FlightAware.
The highly transmissible Omicron strain has sent new cases skyrocketing across the globe, with countries reviving dreaded lockdowns, major sports leagues cancelling Boxing Day football and rugby fixtures, and cruise ships returning to port with Covid-infected passengers.
Governments including the United States are scrambling to boost testing and vaccinations.
In China's Xi'an city, 13 million residents were confined to their homes Sunday amid tightened restrictions as the country recorded its biggest Covid-19 infection numbers in 21 months.
Desperate to keep a lid on outbreaks before February's Beijing Winter Olympics, China has implemented a vigilant "zero-Covid" strategy involving tight border restrictions, lengthy quarantines and targeted lockdowns. But there have been sporadic flare-ups.
In the United States, top pandemic advisor Anthony Fauci warned of a Covid "testing problem" as the virus overwhelms the nation and he vowed to make more tests available next month.
"There are still some issues now of people having trouble getting tested," Fauci told ABC Sunday talk show "This Week."
"But we're addressing the testing problem, he added, saying it should be corrected "very soon."
Still, cases have soared. New York's health department said Covid-19 pediatric hospitalizations have risen four-fold over the past two weeks as Omicron gained hold.
In Florida, health officials say new Covid cases spiked to 125,201 for the week ending December 23, four times its previous week's total.
The state is a global hub for the cruise industry, and US health authorities said dozens of ships were being monitored for possible infection after at least two vessels recorded Covid outbreaks in recent days despite taking comprehensive measures regarding vaccinations.
The Washington Post reported that several ships including the Carnival Freedom -- whose parent company confirmed to AFP Sunday that a "small number" of passengers tested positive onboard -- were denied port in the Caribbean.
"We're sailing on a petri dish," Ashley Peterson, a 34-year-old passenger on the ship, told the Post. "I feel like I just spent my past week at a superspreader event."
Air travel remained the major global travel headache.
Aircrew and ground staff have fallen sick or gone into quarantine after exposure to Covid, multiple airlines acknowledged.
Lufthansa, Delta, United Airlines, British Airways, Alaska Airlines and several others have been forced to cancel flights.
JetBlue said it entered the holiday season with "the highest staffing levels we've had since the pandemic began."
But "despite our best efforts, we've had to cancel a number of flights, and additional flight cancellations and other delays remain a possibility as we see more omicron community spread," the airline said in a statement.
Chinese carriers, notably China Eastern and Air China, have scrubbed more than 2,000 flights over the long weekend, including many going in and out of Xi'an Xianyang International airport, according to tracker data.
Flightaware.com reports nearly 2,900 flights were canceled worldwide on Saturday, and 2,600 and counting on Sunday, with 1,000 of those taking off or landing at US airports. More than 11,000 Sunday flights have been delayed.
The cancellations added to the frustration for many people eager to reunite with their families over the holidays after last year's Christmas was severely curtailed.
The American Automobile Association estimated more than 109 million Americans would travel by plane, train or automobile between December 23 and January 2, a 34 percent increase over the last year.
But most of those plans were made before the detection of Omicron, which has become the dominant strain in the United States, overwhelming hospitals and healthcare workers.
US authorities have recorded an average of over 175,000 new daily cases over the recent period, the Centers for Disease Control and Prevention reported.