King Charles III has hailed the "heartfelt solidarity" of people across the recession-hit UK struggling with a worsening cost of living crisis, in his first Christmas Day message as monarch.

Addressing the country from the Windsor Castle chapel where his mother, Elizabeth II, was interred in September, the 74-year-old also thanked people for the "love and sympathy" expressed following her death.

Standing aside a sparkling Christmas tree, the sovereign noted in the annual pre-recorded royal message -- broadcast at 1500 GMT -- that it is a "particularly poignant time for all of us who have lost loved ones".

He then turned to the impact of the country's growing economic woes, as decades-high inflation eats into earnings and escalates strikes over pay across the public and private sectors.

"I particularly want to pay tribute to all those wonderfully kind people who so generously give food or donations, or... their time, to support those around them in greatest need," Charles said, dressed in a blue suit.

"Our churches, synagogues, mosques, temples and gurdwaras have once again united in feeding the hungry, providing love and support throughout the year."

The king also commended charities for their "extraordinary work in the most difficult circumstances".

He added: "Such heartfelt solidarity is the most inspiring expression of loving our neighbour as our self."

Charles ascended to the throne when Elizabeth died on September 8 after a record-breaking seven-decade reign. 

He also took over as head of state of 14 Commonwealth countries, including Australia, Canada and New Zealand.

- 'Compassion' -

His coronation will take place on May 6 next year, with Buckingham Palace vowing to reflect the monarchy's historic traditions and its modern role.

In his inaugural Christmas message, Charles said both he and his late mother shared "a belief in the extraordinary ability of each person to touch, with goodness and compassion, the lives of others".

"This is the essence of our community and the very foundation of our society," he added, praising public sector workers from the armed forces to emergency responders to teachers.

In a return to tradition for Britain's royals -- interrupted by the pandemic -- they gathered for Christmas Day this year at Sandringham, their private winter retreat in eastern England.

Charles and Queen Consort Camilla, 75, were joined by Prince William and wife Kate -- and their children Princes George and Louis and Princess Charlotte -- at a local church service.

Disgraced Prince Andrew, who has been sidelined over his links to the late US paedophile financier Jeffrey Epstein and claims of sex with a minor, was also among the royals who greeted well-wishers outside. 

However, US-based Prince Harry and wife Meghan were notable absentees, as their ongoing feud with the family shows little sign of abating.

The couple risked deepening the rift -- which first became public when they sensationally quit royal life in early 2020 -- by airing various grievances in a six-part Netflix docuseries this month. 

It follows a series of other broadsides they have launched against the royal family since relocating to California, with more set to come.

Harry will publish a contentious memoir -- named "Spare" -- within weeks.