LONDON (AFP) - A star-studded cast of artists gathered Friday to celebrate Nelson Mandela's 90th birthday at a giant concert in London, in support of his global AIDS campaign.

Queen, Razorlight and Annie Lennox were among musicians performing at the gig for the former South African president's 46664 campaign against HIV/AIDS, to be broadcast around the globe.

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 compered by US actor Will Smith.

British Prime Minister Gordon Brown, Formula One driver Lewis Hamilton and US actor Denzel Washington are among those due to attend the concert, which was to kick off at 6:30 pm (1730 GMT).

"We're particularly honoured that he'll be celebrating his birthday here in London and that he's using his birthday to selflessy fundraise and build further support for his exceptional 46664 charity," said Brown.

"It's entirely characteristic of a great man."

Other performers on the concert bill include Amy Winehouse, Simple Minds, Josh Groban, Joan Baez, Leona Lewis, the Sugababes, Andrea and Sharon Corr, Eddy Grant, Jamelia, Zucchero, South African artists and the Sudanese "war child" rapper Emmanuel Jal.

"When one retires, it means that you have time for birthdays," Nobel Peace Prize laureate Mandela said.

"The reason why Mr Mandela is coming to this concert is that it is his way of saying thank-you to the British people for the Free Nelson Mandela Concert at Wembley in 1988," a 46664 spokesman told AFP.

"It's going to be a night with a mix of performers from the original concert 20 years ago and the new younger generation who wish to show their support for Mr Mandela."

The 46664 campaign aims to raise awareness of the HIV/AIDS epidemic 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 the fight against the pandemic his main cause.

Mandela, who turns 90 on July 18, is now in frail health and has difficulty walking unaided.

Former Free frontman Paul Rodgers, who will be singing with Queen, said: "It's typical of the man's humility that on his birthday he should make this huge effort on behalf of other people."

Tickets for "The 46664 Concert Honouring Nelson Mandela at 90" cost 65 pounds (128 dollars, 82 euros) each.

The first 46664 gig was held in Cape Town in 2003 and three others in South Africa, Madrid and Norway have been held since.

Troubled British soul singer Winehouse remains on the bill, despite recent hospital treatment for traces of emphysema.

"She was in fantastic form at the rehearsal a few days ago," said the 46664 spokesman.

"Everyone is so thrilled and so excited to see Amy singing so well."

Mandela arrived in London on Monday and met Brown at his hotel and had an informal private audience with Queen Elizabeth II on Wednesday.

On Wednesday evening he made headlines at a fundraising dinner by breaking his silence over the crisis in Zimbabwe, describing it as a "tragic failure of leadership."

It was unclear if Mandela would speak during Friday's concert.

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