Thousands of South Africans are demonstrating for the resignation of President Jacob Zuma, who has been enmeshed in scandals that critics say are undermining the country's democracy.

The protests in the administrative capital of Pretoria on Wednesday came as opposition lawyers argued in court for the release of a state watchdog report about allegations that a business family linked to Zuma sought to influence some Cabinet post selections.

Business executives, religious leaders and others have gathered in a Pretoria cathedral to demand that Zuma quit, while separate rallies are also being held by South Africa's two biggest opposition parties.

Zuma has not commented this week on growing calls for his ouster. He is scheduled to chair a forum in Harare on Thursday with Zimbabwean President Robert Mugabe.