From Billie Eilish in New York to BTS in Seoul and Elton John in Paris, one of the biggest-ever international charity events was set to kick off Saturday with concerts around the world to raise awareness on climate change, vaccine equality and famine.

Global Citizen Live, a series of concerts from more than 60 artists in London, Lagos, Rio, Sydney, Mumbai and beyond, will be broadcast globally from 1700 GMT for a full 24 hours.

Eilish, Coldplay and Jennifer Lopez will perform in New York's Central Park, where Britain's Prince Harry and Meghan Markle will also be on stage.

Stevie Wonder will play in Los Angeles, while Ed Sheeran will headline in Paris alongside Elton John, Black Eyed Peas and Stormzy.

Tens of thousands of spectators are due to attend the biggest concerts, on condition of vaccination proof or negative COVID tests.

There will also be pre-recorded performances from a huge number of stars, including BTS in South Korea, 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 -- will also be broadcast as part of the event.

"Across six continents, artists will help rally citizens in demanding that governments, major corporations and philanthropists work together to defend the planet and defeat poverty," NGO Global Citizen said in a statement.

It said it was focusing "on the most urgent, interrelated threats hitting those in poverty the hardest -- climate change, vaccine equity, and famine".

- Pressuring governments -

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

The organisation 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.

Global Citizen 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.

Tickets to Saturday's shows were distributed free of charge to randomly selected people who signed up for the app and shared its petitions and messages on social media.

The head of the World Health Organization, Tedros Ghebreyesus, lent his support to the latest campaign, urging vaccine equality.

"We now face a two-track pandemic of haves and have-nots," he said.

"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".