Though a victory is expected for the African National Congress, the party is less sure of whether it can hold onto its two-thirds majority in what has become South Africa's most contested election since the country's first multiracial vote in 1994.
Parliament elects South Africa's president by a simple majority, putting Zuma in line for the post when the new assembly votes in May.
The ANC views Zuma as the first leader who can energize voters since the legendary Nelson Mandela. But critics say Zuma is too beholden to unions and leftists, and will not be able to fulfill promises of creating jobs and a stronger social safety net amid the global recession.
Preliminary results from the 4.88 million ballots counted so far yesterday showed the ANC leading with 65 percent. A record 23 million South Africans registered to vote and polling officials said the turnout could be more than their pre-vote estimate of 80 percent. The largely white opposition Democratic Alliance, according to the preliminary count, had about 18 percent. It was expected to take South Africa's richest province, the Western Cape, from the ANC.
The Congress of the People - formed by a breakaway faction of the ANC last year - was trailing with just under 8 percent in preliminary results, despite expectations at one point that it would post a serious challenge to the ruling party. Turnout was heavy, and some stations had temporary ballot shortages or struggled because ballot boxes filled so quickly.