Thousands of university and secondary students in Hong Kong skipped the first day of classes as part of ongoing pro-democracy protests in the city, organisers said.
Images on social media and in local media showed students wearing masks in the city's centre and outside their respective schools.
Protests in the administrative region escalated in June in opposition to an extradition bill that would have allowed Hong Kong citizens to be extradited to mainland China.
Now protesters want an end to police violence and are calling for chief executive Carrie Lam to step down.
Video of riot police confronting protesters emerged in what appeared to be some of the most violent exchanges since the beginning of the protests.
A protest had been cancelled by the Civil Rights Human Front—a group of almost 50 pro-democracy groups—after they weren't able to get authorisation from police, but thousands protested anyway over the weekend.
A gathering organised by the student union at the Chinese University of Hong Kong continued despite objections from the university which said it was high risk.
The student union at the university wrote on Facebook that the protest would continue despite the university objections: "we reiterate that the right to express our discontent towards the regime through class boycotts should be respected. No matter how difficult times are, we shall never surrender and will die fighting for the freedom from fear."
Rocky Li, a student at the Hang Seng School Of Commerce who joined protests on Monday, told Reuters: "you know every day I can study at home or in the classrooms, but I skip one classes to express my voice and opinion to Hong Kong. It's more important than I study in the classrooms. So I'm right here."
Another student, Michael Chan at the Hong Kong University of Science and Technology told Reuters: "We don't want our children to live under a society that is really unfair, injustice. And I think this is the minimum that we can do, and to skip our classes and to join this event."
Medical staff at several hospitals in Hong Kong also protested, forming a human chain and staging a sit-in.