The protesters apparently took test papers away from students who were sitting for a test. Police used rubber bullets to disperse the crowd.
Some students were seen gathering test papers that had been torn up by protesting students.
Wits spokesperson Shirona Patel said the group were disrupting classes at the west campus and the medical school. She said a chemical engineering test was disrupted.
Security and police officers were attending to the incident.
Earlier on Thursday, the university said 100 books had been damaged in a fire on Wednesday afternoon.
Apology to staff, students
The fire was started in the last aisle on the second floor of the Wartenweiler Library, Patel said in a statement.
“Security has determined that the fire was started with an accelerant or flammable substance, which may have been hidden in a bag found on the scene,” Patel said.
The fire was extinguished and a high level investigation was underway by Wits security and the police.
Patel said academic activities at the university were underway.
“We apologise to all staff and students who were affected and evacuated yesterday [Wednesday].”