South Africa's firebrand ANC Youth League leader Julius Malema was found guilty on Monday of hate speech for singing an apartheid-era song that called for the killing of white farmers.

The verdict against Malema, one of the country's most prominent politicians, comes as he is fighting for his political survival in a separate disciplinary case brought by the ruling African National Congress (ANC), which has charged him with bringing the party into disrepute.

No justification exists allowing the words to be sung, said Judge Collin Lamont.

Malema was ordered to pay some of the court costs in the civil case that did not carry a criminal penalty.

Malema, 30, was not in court when the decision was read. He sang Shoot the Boer at a number of public events last year.

His regular calls to nationalise mines and seize white-owned land have unnerved investors but struck a chord with poor blacks who see him as a future leader of Africa's biggest economy.

The case was brought to the South Gauteng High Court by the Afrikaner civil rights group Afriforum, which said white farmers felt threatened by the song's lyrics.

Judge Lamont said words were powerful weapons and ordered Malema and the ANC to stop singing the song in public or private. The ANC has argued the song was a part of the historical struggle against oppressive white regimes and should not be banned.

Lamont said the song had no place in the new South African society where the enemy has now become a friend.

People must develop new customs in an open society by giving up old practices that are hurtful to the people who share it with them.

For the ANC premised on non-racialism, the ruling casts uncertainty on the future of other struggle songs with lyrics either aimed at striking fear in the former white enemy or calling for the minority population to be overthrown.

The ANC said in a statement it respected the decision but had questions about the judge's arguments.

We view this judgement as an attempt to rewrite the South African history which is not desirable and unsustainable, said the statement issued by ANC spokesman Jackson Mthembu.

Analysts said the civil case would not have serious political implications for Malema and could strengthen his support among the poor black majority who have seen little improvement in their economic fortunes after apartheid ended.

Malema's die-hard supporters don't care about the courts and not much will change in the ANC. It makes no difference to those intent on disciplining him, said Prince Mashele, executive director of the Centre for Politics and Research.

Malema, the son of a former maid, is facing a criminal investigation over his finances. He has often railed against the country's white minority, whom he accuses of being criminals.

The ANC's disciplinary hearing against Malema meets again on Tuesday. If he is found guilty, he could be suspended or expelled from the party that dominates the country's politics.

There are people in the ANC like President Jacob Zuma who see him as thorn in their flesh so they would want him punished harshly, said Mashele.

The hearing is a high-stakes gamble for Zuma. If Malema is exonerated, Zuma could be fighting for political survival as Zuma's foes court the youth leader in their bids for power.