South Africa's President Thabo Mbeki has warned members of the governing African National Congress that they are not meeting to choose his successor.
Thabo Mbeki will step down as president in 2009
Delegates in the hall were seen parading posters of a front-runner and the former vice-president, Jacob Zuma.
The four-day policy conference is threatening to be overshadowed by the question of who succeeds him after 10 years as party leader in December.
They would then be the favourite to be president of the country in 2009 polls.
"This policy conference... has nothing to do with who is or will be a leader of the African National Congress (ANC)," he told the 1,500 members gathered in Midrand.
Mr Zuma, who is still ANC deputy leader, and the business tycoon, Tokyo Sexwale - have shown an interest, although in keeping with party tradition, they are not actively campaigning.
The ANC has dominated South African politics since it ended white rule 13 years ago, but observers say there is increasing dissatisfaction with the growing gap between rich and poor, at a time when the economy is booming.
Addressing the conference, President Mbeki said there was a limit to what the ANC could achieve in the time it had been in power:
"It is not possible to solve problems that have accumulated over 350 years in a mere 13 years of our democracy."
Mr Mbeki and his ANC deputy Mr Zuma are putting up a united front
Mr Sexwale also made a plea to the ANC for the race to be open and honest.
"There is a growing tendency to carry out dirty character assassinations and the dissemination of lies about other comrades. This has reached uncontrollable proportions," he said quoting from an internal ANC document warning of the danger of dishonest politics.
The ANC leader must first be nominated by ANC branches around the country and other candidates are certain to emerge in the coming months.
But BBC reporters in Johannesburg say all the key candidates will be lobbying very hard over the next four days if they want to succeed.
The ANC has been experiencing serious internal division, and there is a strained relationship with its traditional alliance partners - the Congress of South African Trade Unions and the South African Communist Party.
Much of the debate has centred around the widening gap in South Africa between rich and poor.
An ongoing strike by public servants, which has so far cost the economy an estimated $418m, is among them.
Earlier Mr Sexwale said the various policy discussion documents promised robust debate.
"Contrary to speculations from our critics, the ANC is open to acknowledging even some of the most difficult issues around existing antagonisms and tensions which threaten to undermine our very own organisational unity."
The demands from the left of the governing coalition have created tensions within the business-friendly wing of the ANC led by President Mbeki.
Policies that will be discussed in the four-day conference will help determine whether or not the ANC will rule successfully in the next decade or so, our reporters say.
As the continent's economic power house, the way the party resolves its internal tensions will have an impact on the business climate, they say.