The ANC secretary general says students protesting fee increases are not doing anyone a favour by studying.
The building is the main space where students hold mass meetings and they pushed their way in after police and security officials tried blocking them.
Wits students are planning to shut down the university, but the situation at other institutions such as Stellenbosch has been sedate.
Students vow to retaliate after private security and SAPS officials barred them from entering the venue where they intended to hold a mass meeting.