The campus of a Hong Kong university transformed into an apocalyptic scene on Monday as riot police armed with tear gas and rubber bullets surrounded pro-democracy protesters.

The standoff between authorities and protesters at Hong Kong Polytechnic University has turned into one of the fiercest, most violent conflicts in the nearly six months of protests in the autonomous territory.

What began as a movement to block a controversial extradition bill morphed into a sustained call for greater democratic rights in Hong Kong and a pushback against the growing influence of China. The demonstrations have grown increasingly tense in recent weeks. Last week, police shot a protester and demonstrators set a pro-Beijing activist on fire.

Protesters have been occupying parts of the Hong Kong Polytechnic University campus since last week, but the confrontation with police escalated dramatically on Sunday and into Monday, turning the campus into a war zone. Protesters hunkered down and barricaded themselves against police, flinging firebombs and debris and even firing arrows at riot police. Police threatened to use live ammunition in response.

Early Monday local time, riot police rushed the campus, effectively trapping hundreds of demonstrators inside. Authorities cornered the activists and delivered an ultimatum, calling on them to surrender or face a barrage of tear gas. Police said those who do surrender will face arrest and potential charges of rioting, which means individuals could face up to 10 years in prison.

Some demonstrators have managed to sneak away; photographers documented people running along a footbridge away from campus. But others are holed up, waiting for an opportunity to break free and avoid arrest.

Han, a 23-year-old protester and first aider, told me she was hiding inside a classroom at Hong Kong Polytechnic University, resting before trying once again to find a way out. We spoke through a translator based in the UK via WhatsApp.

Han said that protests broke out at PolyU because it’s near major infrastructure; protesters wanted to block those areas to create real impact and force the government to listen to their demands. “Students [don’t] want to fight these battles, they just want the government to listen to their demands,” she said.

Some protesters pleaded for help on social media, saying they were cornered by police with no defense and running out of food and medicine. Supporters of the campus protesters tried to form a human chain to deliver medical supplies, helmets, food, and water. According to the Wall Street Journal, the link stretched miles but failed to penetrate the police barricade.

Hong Kong officials said they were allowing the Red Cross to enter the campus and treat injured protesters.

Other supporters -including parents of some students at the university -staged a sit-in outside campus. They carried signs that said “Save our Kids.”

Demonstrators also flocked to other parts of the city, trying to distract and draw police away from the campus so demonstrators there could escape. Scenes of chaos also emerged in other parts of Hong Kong as demonstrators blocked traffic, many carrying umbrellas to fend off tear gas.

The Hong Kong protests are growing increasingly tense, with no obvious solution in sight

At least 150 people were arrested over the weekend, according to the New York Times. That number is likely to rise, though, as about 500 protesters were still believed to be trapped inside campus well past midnight local time.

Police said they had arrested more than 50 people who “claimed to be journalists or medics” on Monday, according to the Hong Kong Free Press. The BBC reported that, per Hong Kong’s Hospital Authority, more than 100 people had been injured.

And authorities seem prepared to outlast the protesters. Cheuk Hau-yip, the regional police commander, threatened arrest for anyone on campus, saying officers had given protesters “enough time and enough warnings.”

“If they surrender and come out, we will arrange the appropriate medical help for them,” Cheuk said, according to the Washington Post.

Tensions between police and protesters have fueled the protests in recent weeks, as pro-democracy activists accuse authorities of using heavy-handed and violent tactics to crush otherwise peaceful protests. Police, in turn, point to very real examples of vandalism and violence as part of the demonstrations to justify the use of force. Demonstrators say they’re just trying to defend themselves.

That has led to specific demands from the protesters, including releasing all those arrested for rioting and an independent inquiry of the Hong Kong police force. The Hong Kong government, led by Chief Executive Carrie Lam, has so far resisted, saying the current body is equipped to handle a review.

This impasse has created an untenable situation in Hong Kong -though some protesters see the police response as galvanizing Hongkongers. “The unacceptable use of violence by the police is pushing more people, i.e. supporters of peaceful protests, to believe they [should] come out and protect the students,” Han said. “So I do think all these protesters’ operations [are] leading to a positive outcome.”

Also on Monday, a Hong Kong court ruled that the government’s face-mask ban -introduced last month -was unlawful. Though many protesters had been defying the ban anyway, it was another example of the Hong Kong government’s botched and aggressive attempt to curtail the unrest.

As the Washington Post noted, Lam has remained largely quiet during the unrest this weekend. Hong Kong has its own government system under the “one country, two systems” rule that has been in place since Great Britain returned Hong Kong to China in 1997 and is supposed to last until 2047. Protesters see Beijing’s encroachment ahead of that date as an existential threat to their territory.

On Monday, the Chinese government warned that “no-one should underestimate” Beijing’s will “to safeguard its sovereignty and Hong Kong’s stability.”

Beijing interceding directly in Hong Kong would inflame tensions, and so far it has stopped short of such measures. But China has grown increasingly impatient with the uprising in Hong Kong, which has hurt the economy in the territory.

The campus unrest also threatens to derail upcoming local elections in Hong Kong, scheduled for this weekend, where pro-democracy lawmakers are expected to win big. Some fear that the Hong Kong government might cancel or postpone the elections, citing the violence in the city.

That would deny Hong Kong a democratic outlet for their discontent -exactly what protesters are fighting to preserve.