King Charles will deliver his Christmas Day message from a church with links to the medical community, Buckingham Palace says, in a break with tradition amid his continued cancer treatment.

The 76-year-old monarch revealed in February that he was battling an unspecified cancer and returned to public duties in April.

Last week, a palace source told CNN that his "treatment has been moving in a positive direction" and "will continue into next year".

The annual festive broadcast is normally recorded at Buckingham Palace or Windsor Castle.

But the British monarch opted to film this year's message at Fitzrovia Chapel in central London, which was previously a hospital chapel before it was demolished in 1924.

Buckingham Palace confirmed the location on Monday afternoon after it was first reported by The Daily Telegraph.

Charles' decision marks the first time in over a decade that the address has not been recorded on the royal estate.

The last message filmed outside a royal residence was in 2006 when the late Queen Elizabeth II recorded her message at Southwark Cathedral.

Fitzrovia Chapel - a beautifully ornate Grade II-listed building featuring Byzantine-inspired architecture - is "now a space for quiet reflection, discovery and celebration, connecting diverse communities from all faiths or none," according to Buckingham Palace.

The venue also boasts unique royal links as King Charles' grandfather, the Duke of York - later George VI - laid the foundation stone when it was rebuilt in 1928 and returned to help open the building when it was completed in 1935.

The chapel was restored between 2013 and 2015.

The choice of location reflects the King's deep spirituality and will be seen as an apt selection in a year when both he and his daughter-in-law, Catherine, Princess of Wales, faced their own health challenges.

The annual speech from the monarch is traditionally recorded earlier in December and broadcast on television and radio at 3pm on Christmas Day in Britain.

New Zealand is the first country in the Commonwealth to broadcast the message, tonight at 6.06pm on RNZ National, and again at 6.50pm on TVNZ's Channel 1.