The broadcast on social media opened with a pre-recorded performance by BTS in Seoul and followed by live performances from around the world, and is to include Billie Eilish, Coldplay and Jennifer Lopez in New York's Central Park,
A "once-in-a-generation" global music event kicked off 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.
NGO 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.
LIGHTS 💡 CAMERA 🎥 ACTION 🎬 #GlobalCitizenLive is officially LIVE for the next 24 hours!— Global Citizen - #GlobalCitizenLive is LIVE NOW! ⭕ (@GlblCtzn) September 25, 2021
Tune in now for this once-in-a-generation festival, featuring @JLo, @5SOS, @bts_bighit, @DojaCat, @alokoficial, @Coldplay, & more performing all over the world! ⭕️ https://t.co/22wCyDtAQS
Tens of thousands won tickets for the concerts (which required vaccination proof or negative tests) by signing up for the Global Citizen app and sharing its messages on social media.
Pre-recorded performances were also delivered by Green Day in Los Angeles, DJ superstar Alok in Rio, Kylie Minogue in London and Andrea Bocelli in Tuscany.
This week's comeback gig by The Fugees in New York – their first in 15 years – was also billed as part of the event.
Global Citizen has been behind other high-profile charity events, including "Vax Live: The Concert To Reunite The World" earlier this year in Los Angeles.
That brought together musicians, actors, celebrities, world leaders and even the pope, in a united call for global vaccinations to fight Covid-19.
The organisation describes itself as a movement with a mission to end extreme poverty by 2030.
Its app uses incentives such as concert tickets to encourage users into pressuring governments on issues around sustainability and equality.
Saturday and Sunday's event also brought charitable pledges from international companies like Lego and Cisco.
The head of the World Health Organization, Tedros Ghebreyesus, lent his support to the campaign, urging vaccine equality.
"We now face a two-track pandemic of haves and have-nots," he said ahead of the event.
"We cannot disregard this gross inequity or become complacent."
Elton John almost had to cancel his performance following a hip injury, but said he said he would wait until after the Global Citizen Live gig for his operation "as I don't want to let a charity down".