LONDON, June 27, 2008 (AFP) - A star-studded cast of artists helped Nelson Mandela to celebrate his 90th birthday with a giant concert in London on Friday in support of his global AIDS campaign.

Queen, Amy Winehouse and Annie Lennox were among the performers at the Hyde Park gig for the former South African president's 46664 campaign, which was being broadcast around the world.

Addressing the crowd, a visibly frail Mandela, who had to be helped to the podium on stage, said: 'Where human beings are being oppressed, there is more work to be done. Our work is for freedom for all.

'It is time for new hands to lift the burdens. It is in your hands now. I thank you,' Mandela, who turns 90 on July 18, added.

Following an opening performance from Jivan Gasparyan, an Armenian duduk wooden flute master, US actor Will Smith introduced Anglo-Swedish rockers Razorlight.

Scottish singer Lennox, wearing a t-shirt reading 'HIV positive,' gave an impassioned speech about combating the virus.

'Don't you think that every child should have the right to life?' she said, to huge applause.

The Eurythmics vocalist then performed an acapella song with a choir from the Agape children's orphanage in South Africa, where most residents have lost their parents to AIDS.

Queen and Paul Rodgers were set to rock the audience later before a finale of 'Free Nelson Mandela' featuring Winehouse and the song's writer, Specials keyboard player Jerry Dammers, plus all the artists.

Mandela made headlines on Wednesday by breaking his silence over the electoral violence in Zimbabwe, describing it as a 'tragic failure of leadership.'

Zimbabweans voted Friday in a run-off presidential poll with veteran incumbent Robert Mugabe left as the only candidate after violence against the opposition forced his rival Morgan Tsvangirai out of the race.

Some campaigners have called on Mandela to elaborate on his comments.

'I'm here to see Nelson Mandela,' said Ben Motsumi, 45, a nurse from Klerksdorp in South Africa, who came to the concert with his wife and children.

'He's a hero to me. I've got all pictures of him in my house. I've been in Britain for nine years. This is an incredible occasion for us. If it wasn't for him, we wouldn't be here,' he told AFP.

Other performers on the concert bill include Simple Minds, Josh Groban, Joan Baez, Leona Lewis, the Sugababes, Eddy Grant, Jamelia, Zucchero and the Sudanese 'war child' rapper Emmanuel Jal.

A 46664 spokesman told AFP that Mandela was attending the Hyde Park gig to thank the British people for a concert at London's Wembley Stadium in 1988, which called for his release from jail.

'At the original one, there was anger involved because of the circumstances,' Simple Minds frontman Jim Kerr told reporters.

'This time, there's a lot more joy. It's a unique occasion.'

Precisely 46,664 tickets -- after Mandela's prison number during his 27-year incarceration for trying to topple South Africa's apartheid regime -- went on sale for the three-and-a-half-hour concert.

Formula One driver Lewis Hamilton, Genesis legend Peter Gabriel and British actor Stephen Fry were among the celebrities introducing the artists.

Mandela, who retired from public life nine years ago, is expected to retreat further from the limelight after his birthday celebrations and hand over the reins of his 46664 campaign.

The 46664 campaign, which has seen four previous multi-artist concerts, aims to raise awareness of the HIV/AIDS pandemic, which is rife in sub-Saharan Africa.

South Africa is one of the countries worst-hit by HIV, with 5.41 million people living with the illness. Mandela lost a son to AIDS in January 2005 and has now made fighting the syndrome his main cause.

'I came to support a great man and a great cause,' said Lisle Lewis, 34, from Cape Town, who came with her friend Cindy Noble, five months pregnant, to see Mandela in the flesh for the first time.

'I came to say thank-you. Mandela means freedom, understanding and love. I'm going to start crying in a minute!' the dentist told AFP.

'He's taught me to be more appreciative and accepting of other races.'

Noble added: 'The baby can say he or she heard Mandela.'

Tickets for 'The 46664 Concert Honouring Nelson Mandela at 90' cost 65 pounds (128 dollars, 82 euros) each. The concert was being streamed live on the 46664.com website.