Around 100 others who tried to leave the Polytechnic University were met with tear gas and rubber bullets. Some were arrested.
Authorities say 116 people were injured in the violence on Monday.
In the past week, the campus has become the latest battleground for long-running anti-government protests.
The violence is some of the worst seen during months of unrest in the semi-autonomous Chinese territory. The protests started over a controversial extradition bill, and have now evolved into broader anti-government demonstrations.
China has warned that "no-one should underestimate [its] will to safeguard its sovereignty and Hong Kong's stability", and its ambassador to the UK said the central government would not sit back and watch if the situation became "uncontrollable".
Hong Kong is a part of China, and the protests are, in part, about the fear that the special freedoms the territory enjoys as a former British colony are being eroded.