Hong Kong has announced that all schools including kindergartens will be closed on Thursday as the territory faces another day of escalating unrest.
The Education Bureau announced the unprecedented step on Wednesday, citing safety reasons.
Officials said schools would remain open for children needing supervision.
The Chinese University of Hong Kong also said it would cancel classes for the rest of term after a violent standoff between police and protesters.
The university, one of Hong Kong's most prestigious, saw clashes overnight on Tuesday as police fired tear gas and rubber bullets at masked protesters, who in turn started fires and threw petrol bombs.
Clashes then continued in different parts of the city, just hours after a senior police officer said Hong Kong had been pushed to the "brink of a total breakdown".
The police decision to enter campuses signalled a shift in strategy, correspondents say, as they have largely avoided clearance operations at schools and universities.
Throughout the night there were chaotic scenes of explosions, smoke, and the firing of rubber bullets. Scores of people were injured, reports said.
"This is not only to defend the Chinese University of Hong Kong. It represents the human spirit of defending political freedom and the rights which should be enjoyed by Hong Kongers," one student told the BBC.
Paramedics were treating at least 70 people after the clashes, local media reported, with at least four seriously hurt.
About 142 people have been arrested since Tuesday, raising the total number to more than 4,000 since the unrest started.
In a statement, China's liaison office in the territory said Hong Kong was "sliding into the abyss of terrorism", and urged the government to toughen its crackdown.
What's the university situation now?
Images on Wednesday showed students and demonstrators still at the Chinese University (CUHK) campus, some armed with petrol bombs or other weapons including bows and arrows.
Police displayed some of the arrows at a press conference, claiming they could have pierced officers' protective gear.
CUHK is not the only campus involved.
At universities across the city, anti-government protesters fortified barricades and stockpiled food and projectiles on Wednesday, as police said the violence had reached a "very dangerous and even deadly level". There are fears more clashes could follow.
In a statement, CUHK said it was shortening the academic term and would not resume classes until 6 January 2020, "in view of the escalation of social movements across the territory, the continuous disruption to public transport services [and] the severe damage done to facilities".
Police said they had assisted a group of mainland Chinese students who wanted to leave the campus for safety reasons but were unable to do so due to "roadblocks set up by mobs".
Pictures circulated on social media showing a crowd at Ma Liu Shui Ferry Pier waiting to board a police boat.
Several other Hong Kong universities, among them Open University and City University, said they had cancelled Thursday's classes.
Many went further and closed for the rest of the week. Baptist University suspended on-campus classes entirely until the end of term on 3 December, saying it would replace some with online sessions.
What happened elsewhere on Wednesday?
Protesters called for a third day of strikes with disruption at several metro stations, leading to a morning of long delays and queues.
Activists continued to block roads and build barricades, causing confrontations with police in Yuen Long.
Fresh lunchtime protests in the financial district saw crowds gather to chant slogans. Some black-clad protesters also vandalised a branch of the mainland Bank of Communications.
A session at the city's parliament, known as the Legislative Council, was briefly suspended after opposition politicians angrily questioned the security chief over alleged police brutality.
Why the spike in anger?
This week has seen a marked escalation in violence with intense street battles, violent clashes at universities and flashmob lunchtime protests in the financial heart of Hong Kong.
It is the first time in weeks that protests have taken place during weekdays.
Monday's protests followed a weekend of vigils and demonstrations after a 22-year-old student protester died on Friday.
Alex Chow had been in hospital since he fell from the ledge of a car park during a police operation a week ago.
Later on Monday, violence escalated further when a police officer shot an activist in the torso with a live bullet and a pro-government supporter was set on fire by protesters.
Why are there protests in Hong Kong?
Hong Kong is part of China but as a former British colony it has some autonomy and people have more rights.
The protests started in June against plans to allow extradition to the mainland - which many feared would erode the city's freedoms.
The bill was withdrawn in September, but the demonstrations continued. They now call for full democracy and an inquiry into police actions.
Clashes between police and activists have become increasingly violent, and in October the city banned all face masks.