Johannesburg: The former premier of South Africa's richest province resigned from the ruling African National Congress and said he would join a dissident group threatening to form a breakaway party.

The creation of a splinter group would be the most serious division in the 96-year history of the ANC, which has ruled unchallenged since the end of apartheid in 1994, and would raise questions about the political direction of Africa's biggest economy.

Mbhazima Shilowa, who had stepped down as Gauteng premier in protest against the ANC's removal of former President Thabo Mbeki, said he would support the breakaway group led by former Defence Minister Mosiuoa Lekota.

Shilowa is one of the ANC's most respected officials and a favourite among the business community.

As former premier of South Africa's financial and industrial heartland, and home to the capital, Pretoria, Shilowa could add weight to the dissidents.

"I have decided to resign my membership from the ANC with immediate effect and to lend my support to the initiative by making myself available on a full-time basis as a convener and volunteer-in-chief together with comrade Mosiuoa," he said.

The dissidents have made a wide appeal to South Africans to attend a congress next month to discuss grievances against the ANC and to strategise.