JOHANNESBURG (Reuters) - South Africans vote on Wednesday in the most competitive election since the end of apartheid, with opinion polls suggesting the African National Congress (ANC) will lose its parliamentary majority after 30 years in government.

Then led by Nelson Mandela, the ANC swept to power in South Africa's first multi-racial election in 1994 and has won a majority in national elections held every five years since then, though its share of the vote has gradually declined.

If it falls short of 50% this time, the ANC will have to make a deal with one or more smaller parties to govern - uncharted and potentially choppy waters for a young democracy that has so far been utterly dominated by a single party.

However, the ANC is still on course to win the largest share of the vote, meaning that its leader President Cyril Ramaphosa is likely to remain in office, unless he faces an internal challenge if the party's performance is worse than expected.

Voter dissatisfaction over high rates of unemployment and crime, frequent power blackouts and corruption in party ranks lies behind the ANC's gradual fall from grace.

More than 27 million South Africans are registered to vote at over 23,000 polling stations that will be open from 0500 GMT to 1900 GMT.

Voters will elect provincial assemblies in each of the country's nine provinces, and a new national parliament which will then choose the next president.

OPPOSITION PARTIES

Among opposition parties vying for power is the pro-business Democratic Alliance, which won the second-largest vote share in 2019 and has formed an alliance with several smaller parties to try to broaden its appeal.

Also hoping to gain leverage, the Economic Freedom Fighters, founded by a firebrand former leader of the ANC's youth wing, want to nationalise mines and banks and seize land from white farmers to address racial and economic disparities.

Former president Jacob Zuma is backing a new party called uMkhonto we Sizwe (MK), named after the ANC's former armed wing. Zuma, who was forced to quit as president in 2018 after a string of scandals, has enduring influence, particularly in his home province of KwaZulu-Natal.

The election commission is expected to start releasing partial results within hours of polling stations closing. The commission has seven days to announce final results but at the last election - also held on a Wednesday - it did so on a Saturday.

(Writing by Alexander Winning; Editing by Estelle Shirbon and Gareth Jones)

By Alexander Winning