South Africans voted today (April 22) in an election that poses the toughest test for the ruling African National Congress (ANC) since apartheid ended 15 years ago.

The ruling party is virtually assured a fourth straight win since defeating white minority rule under Nelson Mandela in 1994, and parliament is expected to vote ANC leader Jacob Zuma president after the ballot.

But the ANC faces an unprecedented challenge from opposition parties hoping to capitalise on voter frustration over corruption, poverty and rampant crime, and could lose the two-thirds majority that gives it the right to change the constitution and entrench its power further.

Polling stations opened at 7 am (0500 GMT) with just over 23 million people eligible to vote in national and provincial elections in Africa's biggest economy. Voters began queuing before dawn.

Many analysts believe the ANC, whose anti-apartheid credentials make it the choice for millions of black voters, will win between 60 and 66 per cent of the vote, a result that would cheer investors keen to see the ANC's grip on power loosened.

One key challenge to the ANC comes from a new party formed by those loyal to former President Thabo Mbeki, who was ousted by the ANC amid allegations he meddled in a corruption case against Zuma. The charges were dropped on a technicality.

The first credible black opposition to the ANC, the Congress of the People party (COPE) appears to have some support among South Africa's growing black middle class, but has faltered as it struggles to win over the poor majority.

Polls close at 9 pm (1900 GMT) and first results are expected to start trickling in late tonight. – Reuters