Protect Madiba's Leagacy

Cyril Ramaphosa has won the support of Cosatu, the biggest union federation, to be the ANC party's next leader ©Rajesh Jantilal (AFP/File)

Cosatu general secretary Bheki Ntshalintshali said it had "resolved to support and lobby" for Ramaphosa, a former anti-apartheid activist and trade unionist who helped negotiate the end of white-minority rule in 1994.

The 64-year-old made a failed bid to succeed Nelson Mandela as president in 1999, before becoming a wealthy businessman and then returning to politics.

Cosatu does not have voting power in the ANC, but boasts over a million members.

"We shall work to lobby and influence the ANC structures to support comrade Cyril Ramaphosa," said Ntshalintshali.

Among the other names in the running to succeed Zuma are African Union Commission chairwoman Nkosazana Dlamini-Zuma, who is Zuma's ex-wife, and ANC treasurer-general Zweli Mkhize.

Zuma has shrugged off growing calls to step down after a series of corruption scandals and weakening economic data.

Two weeks ago, he survived a motion of no confidence after a public watchdog raised accusations over his relationship with the Guptas, a business family accused of wielding undue political influence.

Zuma's presidential term expires in 2019.