Clashes have been reported at numerous universities across Hong Kong with police entering some campuses and using tear gas to subdue protesters.
Reports indicated that officers went into the University of Hong Kong (HKU), Chinese University and Polytechnic University.
The events started with protesters blocking a section of Pok Fu Lam Road, outside HKU's Lady Ho Tung Hall, on Monday morning in response to a general strike call.
They then blocked all major entrances to the campus using furniture and other materials, jammed elevators and poured some liquid on the floor to delay police running inside.
Police who arrived to clear the area fired tear gas to take control of the situation and some reports said they entered the university campus to make arrests.
Police did not confirm this, but in a statement said some university facilities were vandalised and due "the rioters’ extensive illegal acts, police has responded with dispersal and arrest operations".
One student said police fired three rounds of tear gas from a footbridge near exit C of HKU MTR Station.
In a social media footage, HKU law professors Fu Hualing and Johannes Chan were seen trying to calm down students dressed in black and wearing face masks, who seemed agitated and angry.
As the professors asked them not to resort to violence and told them the fight for democracy is a long one, one student shouted back: "How many people do we have to sacrifice?"
Some students were crying as Fu and Chan talked to them for several minutes before the group dispersed.
At the Chinese University police also resorted to tear gas as they confronted a group of protesters.
The CUHK students' union said in a social media message that over 50 riot police entered the campus in the morning, and fired shots at the students.
Around midday, a group of people dressed in black blocked the main entrance of the campus and entered into a stand-off with the riot police. As tensions mounted, police fired tear gas to disperse the crowd. The demonstrators then retreated and the police boarded their vehicles and left.
At Polytechnic University, students blocked several entrances to the campus, including a bridge that leads to the MTR station at Hung Hom. Police who arrived to clear the blockades fired several rounds of tear gas.
The campus radio reported that Owan Li, student council member of PolyU, confronted the police multiple times.
It said students were also angry at the university president, saying he did not speak out against police entering campus.
Angry students then vandalised buildings and facilities in the campus. Some students also replaced the SAR flag with another one, which had words "liberate Hong Kong, revolution of our times" on it.
In a statement, police admitted they had entered into the Chinese University and Polytechnic University campuses, saying some rioters had sought refuge inside the two campuses after engaging in violent acts nearby.
The force said according to the Police Force Ordinance, officers are entitled to enter into any private premises such as shopping malls or MTR stations should there be reasonable suspicion that a suspect is hidden inside.