South African protesters demanding free university education broke windows, forced open doors and threw human excrement in an effort to disrupt the resumption of classes, a university official has said.

The University of Cape Town reopened on Monday after closing because of security concerns, but police were on campus and used a stun grenade to disperse protesters outside a university building.

Another building was evacuated because of vandalism by protesters who threw sewage in the corridors, the university said.

Separately in Johannesburg, students blocked a road during the morning rush hour and threw stones before returning to their residential building at the University of the Witwatersrand.

Many South African universities have been hit since last month by sometimes violent protests for free education.

However, many students want to study and complete the academic year.

AP