King Charles III has become the first reigning king of Australia to visit the country.
The monarch, accompanied by his wife Queen Camilla, arrived at Sydney Airport about 8:30pm, marking the royal couple's first royal tour to Australia since 2018.
His mother Queen Elizabeth II became the first reigning monarch to tour the country when she visited in 1954.
Prime Minister Anthony Albanese was among those to greet King Charles III on his arrival. (AAP: Dean Lewins)
Among those who greeted Charles and Camilla were Governor-General Sam Mostyn, Prime Minister Anthony Albanese and NSW Premier Chris Minns.
Queen Camilla was presented with a posy by 12-year-old Ky, who is living with a serious blood disorder and requested to meet Their Majesties through the Make-a-Wish Foundation, and his sister Charlotte.
A heavy shower just before Charles and Camilla's arrival sent journalists and royal fans ducking for cover.
However, the sideways rain and soggy news crews didn't dampen the excitement of the first reigning king's visit to Australia.
The sails of the Sydney Opera House were also planned to be lit up with a photo montage of the monarchs' previous visits as they flew into Australia.
However, the projections began after they had touched down, delayed by a passing cruise ship.
This visit will be a slimmed-down, five-day affair, taking into account the king's ongoing treatment for cancer, with official engagements in Sydney and Canberra before heading to Samoa on Wednesday for the Commonwealth Heads of Government Meeting.
It is the first visit by a reigning monarch since 2011.
Queen Elizabeth II photographed during her final tour of Australia in 2011. (AAP: David Crosling)
Charles has visited Australia 16 times, the first taking place in 1966 and the most recent visit being in 2018.
Mr Albanese will host a reception for the royals at Capital Hill with Australian political and community leaders, before they take part in a wreath-laying ceremony at the Australian War Memorial.
In 1970, Charles visited Australia for the third time, alongside his parents and his sister for a royal tour. (Facebook: The Royal Family)
Charles, who has a longstanding personal passion for the environment, will tour the National Botanic Gardens on Black Mountain.
He will then have a meeting with scientists at the CSIRO about researching the impact of bushfires and the resilience of the environment to bounce back from devastation.
The Queen will meet family and domestic violence advocates and representatives from the organisation GIVIT, which helps distribute donations across a range of charities.
Charles and Camilla on their most recent tour to Australia. During their official visit they visited the Lady Cilento Children's Hospital in Brisbane. (AAP: Patrick Hamilton)
In Sydney, the king will visit the Royal Australian Navy, which will be on display during a fleet review on Sydney Harbour, where the royal couple will also attend a community barbecue.
The king, who is undergoing cancer treatment in London, will meet with Australians of the Year Georgina Long and Richard Scolyer to discuss their world-leading research on cancer treatments before Charles sits down with Indigenous representatives to learn about Australia's First Nations culture and community.
The Queen will also visit a Sydney library.