"A few days ago, the United Nations estimated that more than 33 million people around the world are living with HIV. This lower figure suggests that prevention programmes have been successful in bringing down infection rates," Mandela said.
"That trend is encouraging but it is still alarming that for every person that receives treatment there are four others that are newly infected," he told the crowd.
Elsewhere in Africa, events were also held to mark World Aids Day. In Niger, around 3,000 people, mostly women and young people, marched through the capital Niamey to demand more measures to help AIDS sufferers.
In the small West African state of Benin, President Thomas Boni Yayi headed a march to show solidarity for AIDS victims.
The Johannesburg concert was to include performances from singers Peter Gabriel, Annie Lennox, and Corinne Bailey Rae and its proceeds will go towards HIV/AIDS programmes throughout southern Africa, the epicentre of the worldwide AIDS epidemic.
The government relented to pressure and launched a plan to provide life-prolonging anti-retroviral drugs in 2003, after Mbeki had questioned the safety of the medication and expressed doubts about widely accepted science on the link between HIV and
AIDS.
But activists have complained that the programme is moving far too slowly, causing several hundred deaths each day. Some 700,000 HIV patients are without treatment, especially bad in rural areas where clinics are saturated with a backlog of cases.
Archbishop Desmond Tutu, who took on South Africa's apartheid government as the country's first black bishop and won the 1984 Nobel Peace Prize, said the battle was far from won.
"We face a monumental crisis, one that was horribly exacerbated when we wasted valuable time in futile academic discussions and debates about the causes of AIDS," he said in a speech to diplomats on Friday.
"We were fiddling whilst our Rome was burning. People who would have been alive today, died needlessly."
