South Africa's main opposition party the Democratic Alliance on Sunday elected Mmusi Maimane as its first black leader, a major step in its efforts to challenge the ruling African National Congress (ANC).

"Your new leader is Mmusi Maimane," outgoing leader Helen Zille announced to loud cheers at the party's annual conference, after she opened a sealed envelope containing the election results.

Maimane, 34, the party's parliamentary leader, was seen as the clear favourite to succeed Zille in the election, in which 1,425 delegates from across the country voted by secret ballot.

Their new leader was raised in the township of Soweto -- heartland of the anti-apartheid struggle -- and joined the Democratic Alliance (DA) only in 2009.

In 2014 he was elected as the party leader in parliament, with Zille's backing, and he has on several times locked horns with the ruling ANC lawmakers, including President Jacob Zuma.

Sunday's vote marked "a milestone for the DA and South African politics", according to an editorial in the Sunday Times.

Zille, a charismatic former journalist and anti-apartheid activist, led the party for eight years.