King Charles III arrives in Australia on Friday, beginning the most strenuous foreign trip since his cancer diagnosis and a tour showcasing busy barbecues, famed landmarks and pressing climate dangers.

Charles becomes the first reigning monarch to set foot Down Under since 2011, when thronging crowds flocked to catch a white-gloved wave from his mother Queen Elizabeth II. 

The 75-year-old king will spend about 20 hours in the air before his flight lands in Sydney, where a montage of 16 previous Australian visits will beam across the Opera House sails.

Prime Minister Anthony Albanese and other high-ranking officials will receive him at the airport, and a ceremonial king's flag will be hoisted above many government buildings.  

After six days in Australia -- a schedule pared back to better manage the king's health -- Charles and Queen Camilla will jet across the Pacific Ocean on a rare trip to island nation Samoa. 

Charles is expected to use the Australian leg to highlight the dangers of climate change, a message sure to resonate in a country scarred by bushfires and floods. 

He will later meet scientists at a world-leading cancer research laboratory, another keenly watched stop given his diagnosis in February. 

The visit will undoubtedly bring pomp, ceremony and plenty of media coverage. 

There will be extravagant mass gatherings, including an event in front of the Opera House and a bustling community barbecue. 

But aside from a clutch of staunch monarchists and ardent republicans, public sentiment on the eve of the sovereign's arrival largely sat somewhere between indifferent and unaware. 

"I'd forgotten they were even coming," said 73-year-old Sydneysider Trevor Reeves, summing up the mood in Australia's largest city.

The lucky country

Australia is a land of many happy memories for Charles. 

He first visited as a gawky 17-year-old in 1966, when he was shipped away to the secluded alpine Timbertop school in regional Victoria. 

"While I was here I had the Pommy bits bashed off me," he would later remark, describing it as "by far the best part" of his education. 

Bachelor Charles was famously ambushed by a bikini-clad model on a later jaunt to Western Australia, who pecked him on the cheek in an instantly iconic photo of the young prince. 

He returned with wife Diana in 1983, drawing mobs of adoring fans eager to see the "people's princess" at landmarks like the Sydney Opera House.

In 1994, a would-be gunman fired two blanks at Charles as he gave a speech on Sydney harbour -- a mock assassination staged as a human rights protest.

With six days in Australia and five more in Samoa, it will be Charles's longest overseas tour since starting treatment for an undisclosed form of cancer.

He made a brief trip to France this year for D-Day commemorations. 

Prime Minister Albanese, a lifelong republican, has made no secret of his desire to one day sever ties with the monarchy. 

Following the death of Queen Elizabeth, his government replaced the monarch's visage on the country's $5 note with an Indigenous motif. 

A recent poll showed about a third of Australians would like to ditch the monarchy, a third would keep it and a third are ambivalent. 

For now, at least, the question of a republic is a political non-starter. 

Charles's looming presence has so far done little to stoke republican sentiment. 

He carefully tiptoed around the question on the eve of his arrival, reportedly saying it was ultimately a "matter for the Australian public to decide".