Paris: A "once-in-a-generation" global music event kicked off on Saturday with pop megastars BTS and Elton John launching Global Citizen Live -- 24 hours of shows around the world to raise awareness on climate change, vaccine equality and famine.

The "Rocketman" got things going in Paris, performing hits including "Tiny Dancer" and "Your Song" in front of the Eiffel Tower in a dazzling green suit.

"No one should be left behind," said the 74-year-old pop legend, who appeared despite a hip injury that forced him to cancel the rest of his tour dates this year.

Global Citizen wants one billion trees planted, two billion vaccines delivered to the poorest countries and meals for 41 million people on the brink of starvation.

The broadcast on social media opened with a pre-recorded performance by BTS in Seoul.

It was followed by dozens of live performances from around the world, and is to include Billie Eilish, Coldplay and Jennifer Lopez in New York´s Central Park, where Britain´s Prince Harry and Meghan Markle were also due on stage.

Ed Sheeran was the headliner in Paris alongside Black Eyed Peas and Stormzy, while Stevie Wonder tops the bill in Los Angeles.

"There has never been a greater need for advocacy than right now," said Bollywood star Priyanka Chopra, hosting the live broadcast from Paris.