Christmas has been marked around the world amid a surge in COVID-19 infections that kept many families apart, overwhelmed hospitals and curbed religious observances as the pandemic was poised to stretch into a third year.

Yet, there were homilies of hope, as vaccines and other treatments become more available.

Pope Francis used his Christmas address to pray for more vaccines to reach the poorest countries.

While wealthy countries have inoculated as much as 90 per cent of their adult populations, 8.9 per cent of Africa's people are fully jabbed, making it the world's least-vaccinated continent.

Only a few thousand well-wishers turned out for his noontime address and blessing, but even that was better than last year, when Italy's Christmas lockdown forced Francis indoors for the annual Urbi et Orbi (To the city and the world) speech.

"Grant health to the infirm and inspire all men and women of goodwill to seek the best ways possible to overcome the current health crisis and its effects," Francis said from the loggia of St Peter's Basilica.

"Open hearts to ensure that necessary medical care -- and vaccines in particular -- are provided to those peoples who need them most."

In the United States, many churches cancelled in-person services, but for those that did have in-person worship, clerics reported smaller but significant attendance.

"Our hopes for a normal Christmas have been tempered by omicron this year ... still filled with uncertainties and threats that overshadow us," the Reverend Ken Boller told his parishioners during midnight Mass at the Church of St. Francis Xavier in New York City.

"Breakthrough used to be a happy word for us, until it was associated with COVID. And in the midst of it all, we celebrate Christmas."

In Britain, Queen Elizabeth II noted another year of pain -- particularly personal after losing her husband, Prince Philip, in April -- and urged people to celebrate with friends and family.

"Although it's a time of great happiness and good cheer for many, Christmas can be hard for those who have lost loved ones,'' the Queen said in the prerecorded message broadcast when many British families were enjoying their traditional Christmas dinner.

"This year, especially, I understand why.''

Thousands of people across Britain got a vaccine booster shot for Christmas as new cases hit another daily record of 122,186.

The Good Health Pharmacy in north London was one of dozens of sites that stayed open Saturday to administer "jingle jabs" amid a government push to offer booster shots to all adults by the end of the year.

The head of intensive care at a hospital in Marseille, France, said most COVID-19 patients over Christmas were unvaccinated, while his staff are exhausted or can't work because they are infected.

"We're sick of this," said Dr Julien Carvelli, the ICU chief at La Timone Hospital, as his team spent another Christmas Eve tending to COVID-19 patients on breathing machines.

"We're afraid we won't have enough space."

On the other side of the globe, hundreds of thousands of people in the Philippines, Asia's largest Roman Catholic nation, spent Christmas without homes, electricity, or adequate food and water after a powerful typhoon left at least 375 people dead last week and devastated mostly central island provinces.

Governor Arthur Yap of hard-hit Bohol province, where more than 100 people died in the typhoon and about 150,000 houses were damaged or destroyed, appealed for help.

He was happy many Filipinos could celebrate Christmas more safely after COVID-19 cases dropped, but he pleaded: "Please don't forget us."

COVID-19 testing continued unimpeded in some places, while other sites closed for the day.

Swelling numbers of cases in Florida made tests almost as popular as Christmas ham. Florida hit a new case record for the second day in a row.

Most of New York City's 120 testing sites were closed on Saturday, a day after police were summoned to a Brooklyn neighbourhood to quell an angry crowd that had been expecting to receive free at-home testing kits, only to have the supply run out.

Chairs went empty at some dinner tables after airlines around the world cancelled hundreds of flights as the omicron variant jumbled schedules and reduced staffing.

Airlines scrapped nearly 6000 flights globally that had been scheduled to take off Friday, Saturday or Sunday, with nearly a third involving US flights, according to FlightAware, a flight-tracking website.

At a reception centre for asylum-seekers in Cyprus, Patricia Etoh, a Catholic from Cameroon, said she did not have any special plans because it just did not feel like Christmas without her six-year-old child, whom she had to leave behind.

But she added: "We're grateful, we're alive, and when we're alive, there's hope."