King Charles III this week begins his first tour of Australia as monarch, reigniting debate about whether the country should sever ties with the British monarchy and become a republic.

Charles, who was diagnosed with cancer earlier this year, is pausing his treatment for the nine-day tour, which also takes in a Commonwealth summit in the Pacific island nation of Samoa.

The two-nation visit comes with growing calls for reparations for slavery from Caribbean leaders whose countries are members of the 56-nation club of mostly former British colonies.

In Australia, where Charles is also head of state, anti-monarchist groups have been selling "farewell tour" merchandise to supporters.

The head of Britain's Republic campaign, which wants an elected head of state and has been behind high-profile protests in the UK, including at Charles' coronation, has also made the trip to plan events and demonstrations.

Britain's Daily Mirror newspaper, meanwhile, reported that all of Australia's state premiers have turned down invitations to meet the king at a reception in the capital, Canberra.

There was no immediate confirmation.

But a YouGov poll last year suggested that one in three Australians supported becoming a republic as soon as possible while a similar number want to remain a constitutional monarchy.

Australian Republic Movement deputy chair Adam Spencer insists that support for the monarchy is wavering and that Charles should "not be king of Australian subjects".

The first leg of the October 18-26 tour sees Charles 75, and his wife Queen Camilla, 77, travel to Sydney and Canberra before the Commonwealth Heads of Government Meeting (CHOGM) in Samoa.

The biennial meeting comes as the grouping of mostly former British colonies -- 14 of whom have Charles as head of state -- grapples with questions over its future relevance and modern profile.

At its last summit two years ago in Rwanda, Charles responded to growing calls for countries that benefited from slavery to pay reparations and issue an apology by expressing his "personal sorrow" at the suffering it caused.

But the king stopped short of the more concrete action demanded and British Prime Minister Keir Starmer's spokesman on Monday ruled out paying reparations.

The spokesman added that it was "not on the agenda" of the upcoming meeting.

The Caribbean Community (Caricom) Reparations Commission, however, has promised to push for a "full and formal apology" for slavery and work towards establishing a reparatory justice model.

The Commonwealth meeting will also see member nations choose and appoint the grouping's next secretary-general, a post held since 2016 by Britain's Patricia Scotland.

All three candidates -- Mamadou Tangara of Gambia, Shirley Botchwey of Ghana and Joshua Setipa of Lesotho -- have said they are in favour of reparations.

The visit had originally included New Zealand, where Charles is also head of state, but those plans were scrapped in favor of a slimmed-down itinerary following his diagnosis with an unspecified cancer.

Doctors, reportedly pleased with his progress, are understood to have agreed to briefly pause his treatment to allow him to travel.

Charles and Camilla's public engagements on both legs of the tour will reflect their individual interests.

They are set to discuss climate change impacts with staff at the Australian National Botanic Gardens and see how the country's national science agency researchers deal with the aftermath of bushfires.

Charles is due to meet acclaimed medical researchers Georgina Long and Richard Scolyer.

The pair are credited with saving thousands of lives by developing a way to unleash the body's immune system on advanced melanomas, a form of skin cancer previously considered fatal.

Other highlights of the Australian leg will see the royal couple paying their respects to the country's war dead and attending a barbecue –- a staple of Australian culture.

In Samoa, sustainability and biodiversity will be a theme of the king's visit while the queen will focus on literacy, domestic violence and sexual abuse.

The royal family has made numerous visits to Australia.

Charles's late mother, Queen Elizabeth II, was a dedicated head of the Commonwealth and travelled to Australia on 16 occasions, including the last visit by a reigning monarch in 2011.

Charles's many visits as prince included the two terms he spent as a 17-year-old at a school in the mountains of southeastern Australia.

In 1983 when he visited with his former wife Diana and baby son Prince William, huge crowds gathered to capture a glimpse of the 22-year-old princess.