Agang SA had been a "stillborn" party, African National Congress secretary general Gwede Mantashe said on Tuesday, when Agang's leader Mamphele Ramphele announced she was throwing her lot in with the DA.

"I was listening today of the announcement of a stillborn," Mantashe said in an address to the Black Business Council in Johannesburg.

During the announcement of the merger of Agang and the Democratic Alliance, former president Nelson Mandela had been used as an example of someone who took decisions, often against the opinions of his colleagues.

"Everybody talked about Mandela. They didn't talk about their leader, but they talked about ANC.... You cannot separate Mandela from the ANC," Mantashe said.

Speaking to EyeWitness News earlier on Tuesday, Mantashe said the Democratic Alliance was renting a leader in Ramphele, whom the opposition party has announced is candidate for president candidate.

"Two things: It is a report of another stillborn party. It is dead before it was born, called Agang.... Number two, it is rent-a-black, rent-a-leader. We can't be concerned about that," he said.

The Congress of SA Trade Unions (Cosatu) said Ramphele's acceptance of the DA's invitation had proved it right about Agang SA's prospects when the party was formed.

"When Mamphela Ramphele launched her new 'party political platform' on February 18, 2013, the headline of Cosatu's response was spot on: 'Cosatu sees no future for Agang'," spokesman Patrick Craven said in a statement.

"Just how right we were was proved today, less than a year later."

Craven said Ramphele had found her true political home, as the DA was the party of big business.

This was exactly what Cosatu expected of a person who was the former managing director of the World Bank and chairwoman of Gold Fields.

"DA leader Helen Zille says that there was 'no better person' than Ramphele to lead their election bid, but very few ANC voters will be fooled by this move," he said.

"The DA's policies remain just as bankrupt, including lowering entry-level wages for young workers, weakening the laws which protect workers' rights and attacking the trade union movement."

The African National Congress had a far superior track record of struggle, with the country far more likely to begin its economic transformation under a movement forged in the furnace of the liberation.

Today's announcement that AGANG Leader will front the DA's presidential campaign during elections did not come as a surprise to the APC. For a long while we have been suspecting that AGANG was purely established as a vehicle to lure African vote into the DA.

Our view is that this is a continuation of the DA's black face, white body campaign where they put black people as fronts while they continue to ensure that the interests of their core constituency which is a white minority continues to be served.

The African People's Convention said it was confident African people, who were continually marginalised, would "see through the trick of trying to turn them into voting cattle".

"APC calls upon those who have been misled into [supporting] Agang not to despair, and request all to join a real alternative government of the people which is the APC," it said in a statement.

APC was the only political home of choice capable of delivering on their aspirations, it said.