More than 100 people were allowed to leave the Polytechnic University in the early hours of Tuesday, having been trapped there since Sunday night.
A delegation of secondary school heads - including education sector lawmaker Ip Kin-yuen - had earlier secured a promise from police to allow minors still inside to go home safely. But their identities will be taken and they still face prosecution later.
However, those aged over 16 were immediately arrested and taken to police stations.
Former Legco president Tsang Yok-sing and law professor Eric Cheung also went into the campus, and later came out accompanying about a dozen demonstrators. Tsang said around 50 minors had left, and a similar number of adults.
The university remains surrounded by riot police following Sunday's violent clashes, with temporary fencing put up around the campus. Officers had earlier fired tear-gas and rubber bullets at anyone who tried to leave.
But police allowed the delegation to enter the the campus late on Monday night to try to help 150 or so younger students who were there.
According to the head teachers, the situation in the university is extremely tense. Some protesters say they are not afraid of being arrested but are scared of police brutality during detention.
Last updated: 2019-11-19 HKT 03:30