JOHANNESBURG (Reuters) - South African President Jacob Zuma made a hasty exit from a May Day rally on Monday after the crowd of workers that he was due to address became rowdy, with some booing and chanting slogans against him.

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The labor federation Cosatu abruptly canceled Zuma’s speech and other addresses at the rally it had organized, as TV footage showed scuffles breaking out in the crowd, apparently between supporters who voiced their backing of Zuma and opponents of the president.

Zuma and his entourage could be seen on live TV leaving the podium and being whisked away from the rally, in the central city of Bloemfontein, in a motorcade.

Cosatu, a key political ally of the ruling African National Congress (ANC), last month called on Zuma to step down after his sacking of the finance minister triggered a sovereign credit rating downgrade to “junk”.

Marches calling on Zuma to quit have drawn tens of thousands of protestors but the ANC has rejected such calls ahead of two conferences this year, one where it will chart its policy direction, the other where it will pick Zuma’s successor to lead the party in 2019 general elections.

The May Day public holiday is an important date in South Africa’s political calendar, when party leaders try to woo a working class that has been hard hit by lay-offs in key sectors such as mining.

Zuma has become a focus of mounting public discontent over government missteps, rising unemployment and a stagnant economy.

Cosatu has signaled its preference for Deputy President Cyril Ramaphosa, a former trade unionist turned business tycoon who was the ANC’s key negotiator in the talks that lead to the end of white-minority rule in 1994.

At a separate Cosatu May Day rally, in rural Hectorspruit in the eastern province of Mpumalanga, Ramaphosa’s speech was greeted with loud cheers from the crowd, the South African Government News Agency reported.

Weeks ago, Ramaphosa openly disagreed with Zuma’s decision to sack former finance minister Pravin Gordhan, who was widely respected by markets and regarded as a staunch opponent of the corruption that critics say has undermined the ANC’s moral authority.

Zuma is widely believed to want his ex-wife, Nkosazana Dlamini-Zuma, a former cabinet member who just finished a term at the helm of the African Union, to succeed him.