A video of white university students humiliating black staff has sparked angry protests in South Africa.

The tape, which was made last year and surfaced on Tuesday, includes black cleaners taking part in a supposedly joke-filled mock "initiation ceremony" on their knees eating food that had been secretly urinated on.

Authorities at the University of the Free State said that they are launching a criminal probe into the incident.

Two of the students involved left the university last year and the other two have now been barred from campus.

All classes were suspended to allow emotions to calm after a tense morning of protests during which police used a stun grenade to disperse stone-throwing students.

Five students were arrested and later released.

Mogale Mphahlele, Secretary of National Education Health and Allied Workers Union said: "We cannot allow a situation wherein this institution is like an island, this is like a place wherein racism can be practised.

"We are 13 years in democracy and we don't have a place for such kind of people, otherwise they should leave the country."

The university in the city of Bloemfontein, 400 kilometres south of Johannesburg, is regarded as a bastion for Afrikaaners, who are often most closely linked with white apartheid rule.

University authorities have been trying to implement more racial integration at campus dorms, and it was defiance of this policy that apparently prompted the video.

The South African Human Rights Commission said it was investigating complaints that the university actually condoned and allowed violations of human rights and tolerated racism.

Education minister Naledi Pandor also sent a top official to investigate the matter.

Multiracial elections in 1994 ended decades of white rule but racial undercurrents remain strong even today and permeate almost every aspect of South African society.

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