The leader of South Africa's opposition, the Democratic Alliance, has said she will not stand for re-election at the party's congress next month.

Helen Zille said the "time was right" for her to step aside, adding that the DA would benefit from fresh blood.

She will remain as premier of Western Cape province until 2019.

Ms Zille, a former journalist and anti-apartheid campaigner, has led the party since 2007.

"These kinds of decisions are a long time coming, but in the end they are made suddenly," she said.

Ms Zille was born in 1951 to German immigrants. She has been a staunch defender of South Africa's liberal constitution, keeping a check on the leading ANC party's overwhelming power.

In the past, she has openly criticised President Jacob Zuma and led a campaign to bring him before the courts to face allegations of bribery.

Mr Zuma denied the claims, insisting he was the victim of a "political conspiracy".

The DA's support is mainly concentrated in the Western Cape, which has a large white and mixed-race population, but Ms Zille had tried to make inroads into the black electorate.