Dozens tried to flee the Polytechnic University in the morning after a night of mayhem in the Chinese-ruled city in which major roads were blocked and a bridge was set on fire and a police officer was shot by a bow and arrow.
Hundreds of protesters were holed up on campus, with petrol bombs and other homemade weapons amid fears of a bloody crackdown.
Protesters tried to make another run for it in the afternoon but were met with more volleys of tear gas.
Police urged protesters to "drop their weapons" and leave.
Hong Kong has seen a dramatic escalation of the unrest that plunged the Asian financial hub into chaos for almost six months.
Demonstrators were angry at what they see as Chinese meddling in the former British colony have said they are responding to excessive use of force by police.