HONG KONG — During hourslong standoffs with students this week, the Hong Kong police broke an unspoken rule to keep off campuses.
Confronted by lines of riot police, black-clad students at the city’s largest universities erected makeshift barricades and threw bricks. The police responded by firing nonlethal projectiles for the first time on campuses.
In six months of antigovernment protests, universities around Hong Kong had served as sanctuaries for the students at the core of the movement, homes where they could strategize and classrooms where they could debate politics.
This week, they became medieval citadels under siege.
The most dramatic clash unfolded late Tuesday night at a bridge leading to the campus of the Chinese University of Hong Kong. For hours, police officers fired hundreds of rounds of tear gas and rubber bullets and students hurled Molotov cocktails and bricks, and practiced firing bows with flaming arrows. More than 100 injured students were brought to a makeshift first-aid clinic in a gym.
By targeting campuses, the police have breached the last refuge of the protesters, a move that brings the violence to the heart of the universities and invokes the pivotal and fraught role of student activism in the global history of democracy movements.
“One thing that people have realized is that the protests, the movement, the conflict, is unavoidable,” Gabriel Fung, a 19-year-old second-year student at the University of Hong Kong, said. “It’s going to reach you wherever you are at some point.”
It is at these universities where young leaders and other students have been organizing revolts against the Chinese Communist Party and spreading the pro-democracy ideas that undergird the protests. And here too, that the students discuss the wealth inequality that has led to visions of a bleak future among many of their generation.
In Hong Kong, university administrators and professors now find themselves in a difficult position, trying to preach tolerance and walk a tightrope of furious demands from students, the police and government officials. Two schools on Wednesday ended their semesters weeks early.
“Not a single place in Hong Kong is exempt from the rule of law, and that includes universities,” John Lee, the secretary for security, said Wednesday at a news conference. “Universities are not supposed to be the breeding ground of violence.”
The showdown has been brewing for years, going back to the pro-democracy Umbrella Movement of 2014. And the roots of the protests in many ways harken back to social movements elsewhere.
On mainland China, students have led campaigns calling for sweeping political change, notably in 1919 and 1989. In the United States in the late 1960s and early 1970s, violence broke out on campuses during anti-Vietnam War protests, most horrifically at Kent State University in 1970, when Ohio National Guard troops opened fire on students, killing four and injuring nine.
Student activists in Hong Kong have lived by an exhausting weekly rhythm since the movement began in early June: protest on weekends, show up on Mondays for class, study for exams and apply for internships or jobs in between it all. Many argue with parents who disagree with their politics or tactics. Hundreds have been arrested in recent months and quickly released by the police, as required by law.
It was the death of a university student this month that set off the current round of protests and violence. Chow Tsz-lok, a student at the Hong Kong University of Science and Technology, sustained a fatal injury after falling from a parking garage near a police action on Nov. 4. Thousands attended candlelit memorial rallies last weekend and his photograph is on posters and makeshift shrines all over campuses, since he is now a martyr for other students.
Roiled by the latest unrest, universities canceled classes from Monday to Thursday. That meant protesters were able to hit the streets at dawn on weekdays after sleeping a few hours. On campus, activists have sprayed fresh graffiti, including phrases cursing administrators.
The fraught situation led police officers on Wednesday to organize an evacuation of dozens of mainland Chinese students across the border to Shenzhen, where hotels offered them free rooms.
One graduate student at Hong Kong University said he and others from the mainland still felt safer on campuses than on the streets. He said many students do not openly express pro-Beijing opinions and sometimes avoid speaking loudly in Mandarin, the dominant language back home. (He spoke on the condition of anonymity because of the tensions.)
Some university departments have delayed recruitment drives of mainland and foreign students to come up with new strategies; a drop-off in enrollment by mainland graduate students, who often pay full tuition, would lead to budget problems.
Hong Kong’s public universities, which have more than 86,000 undergraduate and nearly 11,000 graduate students, each have distinct characters. That means the students have occupied different roles in the movement, and the protests have played out in different ways on each campus.
The Chinese University of Hong Kong, with 20,000 students, is considered the most radical campus. Most of its students are Cantonese-speaking locals, some of whom live nearby with their parents in dense apartment blocks. And the campus is located high in the hills of Sha Tin, isolated from the city center, which is an hour’s ride away by subway.
On Monday, the police arrested five students on the campus’s edge, administrators said. The next morning, the police, still at the border, confronted front line students, and clashes took place over 20 hours. Rocky S. Tuan, the president, who has been known for trying to engage with students during the movement, showed up during a lull in the evening to urge the students to be calm.
“You all should know that I really want to help you. I will do everything within my capability,” he said. “It is the university’s responsibility to maintain peace on campus, not the police.”
But as Mr. Tuan began walking away, the police fired tear gas. Mr. Tuan himself was enveloped in the gas. Students set fires to keep the police from advancing, and scores formed human chains to pass along bricks, umbrellas and bottled water to the front lines. Students sitting on one patch of road made gasoline bombs as if on an assembly line.
“It was a savage move and a type of police violence when they tried to encroach on the university,” said Timothy Chow, 23, an engineering student who graduated in June. “This is why we have to protect our Chinese University of Hong Kong.”
“When I saw our compatriots and Chinese University staff being hurt by the police, I felt particularly furious and wanted to come back to defend our university,” he added.
At the University of Hong Kong this week, front-line students also set up barricades and, against the advice of professors, threw paving bricks off balconies, even though it is considered the most establishment of the territory’s schools.
Founded in 1911, it is the territory’s oldest university. Many of its students are foreigners or Hong Kong residents who attended international schools. English is the main language, and the university aims to open a mainland China campus. Among its alumni are many police commanders and Carrie Lam, the territory’s chief executive who is reviled by protesters.
On Monday, the students were on edge in part because the police had taken a student from a dormitory early that morning.
Two liberal law professors, Fu Hualing and Johannes Chan, urged a group of front-line protesters in masks not to resort to violence and to understand that the struggle for democracy was a lifetime commitment, according to video footage. But one masked woman shouted they had no choice, and asked: “How many people are we going to sacrifice?”
“We are better, we are different,” Mr. Fu said.
“But we shall not forgive,” a young man shouted, “we shall not forget.”
On Tuesday, police officers arrived at campus entrances to try to clear the barricades. They fired tear gas, but retreated.
Students have called on the president, Xiang Zhang, to forcefully condemn the police, but he has refrained from doing so, and, unlike Mr. Tuan, rarely holds open forums. On occasion, professors have shown up at the front lines to speak to students, as William Hayward, dean of social sciences, did on Tuesday.
“Obviously, as it goes on and as it gets more polarized, this becomes increasingly a challenge,” Mr. Hayward later said of student engagement. “Some of them do really open up, but at the same time, you know, of course they’re trying to figure out — is he on our side or is he trying to silence us?”
As night fell on Tuesday, students traded shifts at the barricades, walking past a famous eight-meter statue of orange corpses, “The Pillar of Shame,” that memorializes the 1989 massacre of pro-democracy students and workers around Tiananmen Square in Beijing by the Chinese government.
Paul Mozur and Katherine Li contributed reporting.