Johannesburg – Central Johannesburg TVET College students and members of trade union Nehawu were protesting in Alexandra on Monday, police said.
The reason for their protest was not known, Captain Kay Makhubele said.
Students had barricaded London Road and 13th Avenue with burning tyres and garbage.
People were advised to avoid the area.
Makhubele said they were on the scene and would re-open the roads and arrest those responsible.
The college is a public institution with campuses around Johannesburg, including Alexandra, Langlaagte, and Parktown. It offers qualifications including NQF levels two to four, skills courses and learnerships.