Arriving just a week after 121 people were killed in a police raid against a gang in a favela near the international airport, the future king took a cable car up the famous Pao de Acucar (Sugarloaf mountain) landmark.

William was handed the keys to the city by Mayor Eduardo Paes against a stunning backdrop of lush green hills and beaches.

"I'm still the king of Rio, but he'll be very welcome here, sharing the city's throne with me during these days," Paes told journalists.

William's visit comes before he flies to the Amazon rainforest to address global leaders at COP30 UN climate talks.

Paes said the prince was "amazed with the beauty of the city" and had discussed Rio's dramatic landscapes, with favelas clinging to forested hilltops that plunge into the ocean.

"We talked about politics. We talked about the landscape of Rio, he asked a lot about the favelas... the contrast between the favelas and the more affluent areas," said the mayor.

William's three-day visit comes as Rio de Janeiro reels from the horrific police clash with the Red Command criminal organization on October 28. Favela residents accused police of carrying out summary executions, but there is significant public support for crackdowns on the city's powerful gangs.

"I tried to explain to him the security issues of the city. Obviously it's much more deep than something that you can explain in five minutes. But it was a good opportunity to explain," said Paes.

"I think it helps to show that this is an incredible, wonderful place. And that it's worth it to keep fighting for Rio."

William's first visit to Brazil is centered around his annual Earthshot Prize which awards one million pounds ($1.3 million) to five pioneering projects tackling threats to the environment.

The prince will meet local communities, visit several iconic sites, and celebrate young climate leaders, according to Kensington Palace.

His Earthshot Awards ceremony on Wednesday will be a star-studded affair, with Brazilian popstar Anitta, Kylie Minogue, Shawn Mendes and three-time Grammy winner Seu Jorge among those to walk the "green carpet" before performing.

Jason Knauf, the CEO of The Earthshot Prize, told journalists that past winners and finalists had "protected and restored over one million hectares of land and ocean, and just one has brought clean water to over 200 million people."

The heir to the British throne will then fly to the Amazon city of Belem, host of the COP30 climate talks, to participate in a meeting of heads of state on Thursday and Friday.

William will deliver a speech on behalf of the British government and his father, King Charles, said a Kensington Palace spokesman, adding that the prince would also participate in a number of bilateral meetings.