The future king'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.

After three days in Rio he will fly to the Amazon rainforest to address global leaders at COP30 UN climate talks on behalf of his father King Charles.

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.

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 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.

William then visited Rio's iconic Maracana stadium -- Brazil's temple of football -- where he was handed the Brazil jersey by 2002 World Cup winner Cafu.

"There's a lot of stars here," the prince said of the jersey, referring to Brazil's five World Cup wins.

He and Cafu later teamed up with some kids to play against each other on the pitch, before William ran drills with the children and took a successful penalty kick.

William also took part in discussions with young people from Brazil, South Africa and Asia who are meeting in Rio to develop skills to become climate leaders under his Generation Earthshot programme.

"We need a bit more courage. We need you guys to keep that energy going. If we wait for good leaders we are going to wait a long time. You guys are my hope," William said after he questioned young people on the problems their communities face and the projects they are working on to help the planet.

His Earthshot Awards ceremony on Wednesday will be a star-studded affair, with Brazilian pop star 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 where he will give a speech and participate in bilateral meetings.