Stars of the screen, stage and sporting arena paid tribute on Friday to Nelson Mandela, whose visit to London was overshadowed by events in Zimbabwe where disputed elections have just ended.

Hollywood actor Will Smith hosted a birthday celebration concert in front of Mandela, who turns 90 next month, and nearly 50 000 cheering fans in London's Hyde Park.

Smith was joined on stage by Formula One racer Lewis Hamilton and pop acts including Queen, Simple Minds, Amy Winehouse, Leona Lewis, Annie Lennox and Razorlight.

The event was organised to support Mandela's HIV/Aids charity "46664", named after his prison number, and comes 20 years after the London hosted another concert for the statesman when he was still behind bars for his stand against apartheid.

"Twenty years ago, London hosted a historic concert which called for our freedom," a frail-looking Mandela told the waving crowd after they had sung him Happy Birthday.

"Your voices carried across the water and inspired us in our prison cells far away.

"As we celebrate, let us remind ourselves that our work is far from complete. Where there is poverty and sickness, including Aids, where human beings are being oppressed, there is more work to be done.

"Our work is for freedom for all ... We say tonight, after nearly 90 years of life, it is time for new hands to lift the burdens. It is in your hands now, I thank you."

Mandela speaks out
The tribute to Mandela coincided with disputed elections in Zimbabwe, and during his trip to Britain Mandela was urged to speak out against President Robert Mugabe who pushed ahead with the vote despite international outcry.

Opposition leader Morgan Tsvangirai boycotted the poll because of a wave of deadly attacks on his supporters.

During his visit, Mandela uttered just four words of criticism of Zimbabwe in a speech at a dinner -- "tragic failure of leadership" -- and they were enough to make headline news.

Mandela, South Africa's first black president, officially retired from politics nine years ago, but he is still a moral authority admired the world over.

People in the crowd appeared to be at the gig more to honour Mandela than to hear the music.

"I'm here because of the man," said Clive Jones, a 31-year-old theatre technician. "I feel he's done so much for the world, especially with what was happening in South Africa. He is also humble and kind."

Emmanuel Jal, a Sudanese hip-hop artist based in London who sang on Friday, said Mandela was "unique" among African leaders. "He did not love power so much, and left it and gave it to someone else," he told Reuters.

Grammy-winning soul singer Winehouse performed her hit single Rehab as well as Valerie, despite being diagnosed with a "touch of" lung condition emphysema earlier this month.

Sporting her trademark black beehive hair, a black and white dress and high-heeled shoes, the 24-year-old appeared nervous at first but received one of the biggest cheers of the night.

At the close of the concert she was joined on stage by Jerry Dammers, who helped organise the 1988 concert, and many of the other performers.

Accompanied by a raucous audience, they sang Dammers' Free Nelson Mandela, which became an anthem for the anti-apartheid movement in Britain in the 1980s. - Reuters