It was a day of huge stars, musical and political, coming together to throw their weight behind a campaign to end world poverty.

The Live 8 concert series had many stunning moments, from U2's Bono singing "Sgt. Pepper's Lonely Heart's Club Band" with Paul McCartney, to a reunion of Pink Floyd that helped close the London show, just before McCartney took the stage again in front of 200,000 people in Hyde Park.

Perhaps the best moment, however, was an appearance by former South African President Nelson Mandela.

"I say to all those leaders: Do not look the other way, do not hesitate, it is easy to make promises, but never go to action," Mandela said to a global TV audience.

When he walked onstage in South Africa's Johannesburg, thunderous applause rose from the crowd, silencing the iconic leader for several moments.

Delighted concertgoers packed the Johannesburg venue, the only African addition to the Live 8 series, dancing and waving signs demanding "trade justice" and "give us food."

"Africans are involved in helping Africa, which doesn't happen too often," Cameroonian singer Coco Mbassi told The Associated Press before the concert.

"We're presenting a different image of Africa -- showing that Africa has good things to give."

Unlike the concerts in the G-8 countries, most of the South African concertgoers were impoverished.

The event took place in a working-class part of the city and concert-goers did not need tickets to attend.

"The spirit is terrific, it's more a celebration than anything else," said CTV News's Murray Oliver, reporting from Johannesburg.

Live 8 concerts are being held around the world -- in London, Tokyo Philadelphia, Paris, Rome, Berlin, Moscow, Johannesburg, and Barrie, Ont. -- in an effort to focus attention on global poverty and put pressure on political leaders to drop the debt burden of the poorest countries.

The London show arguably featured the best lineup of artists, including the actor Brad Pitt.

He tugged on the heartstrings of the London audience, when he recounted the story of a young woman with AIDS whom he met in Africa.

She grabbed him by the arm and pleaded: "Please bring us the drugs, please hurry."

"Let us be fighters for the lives of her life and the lives of her children -- whatever it takes, whatever the cost," Pitt appealed to the audience.

Musicians such as The Who, Madonna, Dido, Mariah Carey, Annie Lennox, Sting and Coldplay were also part of the London concert.

A child dies every three seconds

In Philadelphia, where actor and musician Will Smith is hosting the city's Live 8 concert, he led a global session of finger-snapping, beginning at 12:05 p.m. ET.

The finger-snapping, or "click moment," represents how often a child dies from the effects of extreme poverty.

"Every three seconds in the poorest countries of the world, a child dies as a result of extreme poverty...Dead -- just like that," he said, snapping his fingers.

"We are calling on the eight most powerful leaders to do what they can to end this daily tragedy. With the stroke of a pen, eight men can make a world of difference in the lives of billions of people."

Earlier in Japan, Iceland's Bjork and U.S. rockers Good Charlotte joined a handful of Japanese bands, drawing a crowd of about 10,000.

"People are willing to go out of their way, because we believe passionately in what this is about," said Bjork, who was making her first live performance in two years.

"Just the acknowledgment of the problem is an important step."

In Berlin, German crowd-pleasers Die Toten Hosen opened the city's concert, entertaining the crowd packed into a wide boulevard through a downtown park.

In Moscow, tens of thousands of fans jammed into a venue off of Red Square, to watch performances from Russian rock bands and the British 1980s dance act the Pet Shop Boys.

More than 150 acts were slated to perform in total worldwide, what Live 8 worldwide producer Harvey Goldsmith called a mixture of "the biggest acts in the world, the best acts in the world and the newest acts in the world."

'Mandate for action'

It's 20 years to the month that Live Aid concerts, raising millions for African famine relief, were held.

Today, performers are taking to the stage in 10 venues around the world for an even more ambitious follow-up.

The Live 8 concerts are the brainchild of Irish rocker Bob Geldof, who hopes to raise awareness of poverty in Africa and to increase pressure on world leaders to tackle the crisis.

In an open letter to political leaders published Saturday in several British newspapers, Geldof said the summit will disappoint the world if it fails to deliver an extra $25 billion US in aid to Africa.

"We will not applaud half-measures, or politics as usual. This must be a historic breakthrough," the letter says.

"Today there will be noise and music and joy, the joy of exuberant possibility. On Friday (the end of the summit) there will be great silence as the world awaits your verdict. Do not disappoint us. Do not create a generation of cynics."

While Live Aid was to raise money for victims of famine in Africa, Live 8 is about raising awareness.

The concerts come four days before leaders of the world's richest nations meet in Gleneagles, Scotland, for a Group of Eight summit.

The finance ministers from the world's wealthiest nations agreed to a historic accord earlier this month, which cancels at least $40 billion US worth of debt owed by poor, developing countries.