A senior African National Congress figure has joined a party which broke away from the ruling African National Congress last year, local radio reported on Saturday.
Saki Macozoma, a prominent businessman who has served in the ANC's decision-making body, joined the Congress of the People (COPE) which has positioned itself as a pro-business party.
"For all of us who have been involved in the ANC for a long time, we have always understood that the ANC was a vehicle that carried out the hopes of the people of South Africa," Macozoma said on SAFM radio.
"I have come to the conclusion that this is not possible in the current circumstances. I think this country needs an alternative. It needs an alternative voice. It needs an alternative government."
The ANC has controlled parliament since the end of apartheid in 1994. It faces its toughest challenge at the polls on April 22 from COPE, which was started by dissidents including former Defence Minister Mosioua Lekota, after the ANC ousted President Thabo Mbeki.
COPE has signalled it will seek to capitalise on anxiety among middle class voters and business over the influence of trade unions and communists in the ANC.
Earlier on Saturday, COPE unveiled its list of candidates for provincial leaders, which included Allan Boesak, a popular cleric who was convicted of fraud but later pardoned by Mbeki.
Last week, COPE chose Methodist Bishop Mvume Dandala as its presidential candidate, raising speculation in the local media that he was a compromise after in-fighting in the new party.
Dandala, 57, could appeal to South Africans who have grown tired of corruption scandals in the ANC, and of the party's record on crime, poverty and the Aids epidemic. - Reuters