King Charles III on Tuesday reportedly told fellow cancer patients "I'm well", as he carried out his first official public engagement since being diagnosed with the condition.

The British head of state appeared relaxed as he and his wife Queen Camilla met patients and staff at the University College Hospital Macmillan Cancer Centre in central London.

He talked to patients receiving chemotherapy at a day unit, including 60-year-old Asha Millen, who has bone marrow cancer.

"I said, 'How are you?' and he said, 'I'm well'," she told reporters afterwards.

Another patient, Lesley Woodbridge, 63, said the king sympathised with her, and added: "I've got to have my treatment this afternoon as well."

Charles, 75, suspended most of his duties in February after cancer was found while he was being treated for an enlarged prostate the previous month.

The exact nature of his cancer has not been disclosed but doctors said last week they were "very encouraged" by the progress of his treatment as an out-patient and "positive" about his recovery.

His daughter-in-law Catherine, Princess of Wales, 42, underwent abdominal surgery in January and said in March that she was receiving chemotherapy.

Again, no details were given about what type of cancer she has. Kate, as she is widely known, is married to Charles's elder son and heir Prince William.

- 'Positive' -

Tuesday's event was the first in a number of planned engagements in the coming weeks and designed to raise awareness of the importance of early cancer diagnosis and highlight innovative research, Buckingham Palace said.

Charles, who succeeded his mother Queen Elizabeth II in September 2022, was officially crowned king on May 6 last year.

He has been seen attending church services since his diagnosis and at selected audiences. He has also continued his official state business.

His treatment will continue but his schedule in the coming weeks will be reduced and subject to medical advice, a spokesperson added.

His engagements will include a state visit by Emperor Naruhito and Empress Masako of Japan in June.

The chief executive of University College London Hospitals group, David Probert, said Charles "deliberately went out of his way to meet as many staff and patients as he could".

Patients were "delighted" to see him, he told Sky News, and described the visit as "incredibly uplifting".

Members of the public last week welcomed the king's return to some duties, praising him for raising awareness about cancer, which will affect one in two people, according to Cancer Research UK.

- 'Huge issue' -

Probert said the king's announcement had led to a surge in people looking up symptoms and seeking out treatment.

"It's a huge issue in today's society," Keegan Gray, 23, a demolitions manager from New Zealand, told AFP on Friday.

"A lot of people have cancer and a lot of people they keep it to themselves, they're a bit shy about it," he added after the news Charles would resume some public duties.

Gray said it was "really beautiful" that the king was raising awareness of cancer and the work of treatment clinics.

Charles and Kate's cancer diagnoses have created a headache for the royal family, with both having postponed public engagements.

William has also taken a step back to support his wife and their three young children, leaving fewer senior royals to fill the schedule.

Camilla, 76, has stepped in to take over many of her husband's engagements. Charles's sister Princess Anne and his youngest brother Prince Edward have also taken on more prominent roles.

Charles's largely estranged younger son, Prince Harry, is no longer a working royal but is expected in London on May 8 to mark the 10th anniversary of his Invictus Games for disabled military veterans.

He will then join his American wife Meghan on a visit to Nigeria.