The judge presiding over the rape trial of South Africa's former Deputy President Jacob Zuma has said he is stepping down to protect the judiciary.

Defence lawyers had argued Bernard Ngoepe might be biased as he issued warrants for a search of Mr Zuma's offices in a corruption case last year.

It is alleged that Mr Zuma raped a family friend - a woman in her 30s - at his home in Johannesburg last November.

Mr Zuma, 63, denied the charges when the trial began in the city on Monday.

He was one of the country's most popular politicians but he was sacked from the government last year. He also faces separate charges of corruption.

Judge Ngoepe announced his decision soon after the trial began.

"For the protection of the credibility of the judiciary... I have decided to step aside," he said.

Rape is not a party

Carrie Shelver

Women's rights activist

Crowds stand by Zuma

Judge Ngoepe expressed fears his decision might imply Mr Zuma had the power to chose who was judging him, but believed the need to ensure impartiality was more important.

"I have concluded that protection of the credibility of the judiciary and above all the acceptability of its judgments are factors which should weigh with me heavily."

The new judge will be one of his deputies but has not yet been named. The trial is to resume on Tuesday.

The BBC's Justin Pearce in Johannesburg says many of Mr Zuma's supporters say he is the victim of a political conspiracy and have accused the judicial system of bias.

Up to 1,000 people had gathered to back the former deputy president outside the city's High Court on Monday.

The immediate area outside the court was cordoned off but some of Mr Zuma's supporters got through.

They were singing, dancing to pro-Zuma pop songs and waving placards. "You are the best JZ," read one.

Veteran campaigner

There was also a separate group of about 50 anti-rape protesters.

Not all the protesters backed Mr Zuma Image source

Not all the protesters backed Mr Zuma

"We are sending out a strong message of support and solidarity to survivors of rape and violence," said People Opposing Woman Abuse spokeswoman Carrie Shelver.

"This sounds like a party," she said, referring to the Zuma supporters. "Rape is not a party."

The alleged victim entered court with a headscarf over her face to shield her from the Zuma supporters.

Mr Zuma is a veteran of the ANC struggle to end apartheid. At one stage he was championed by trade unionists and those on the political left as a likely presidential candidate to succeed Thabo Mbeki.

Mr Zuma remains deputy leader of the ruling ANC although it has been agreed that he should not perform any executive functions.

The charges of rape and corruption, for which he is to face trial in July, appear to have left his political career in tatters.