Hong Kong police stormed into a university campus held by protesters early Monday after an all-night siege that included firing repeated barrages of tear gas and water cannons.

Anti-government protesters barricaded themselves inside Hong Kong Polytechnic University for days, fighting back with gasoline bombs and bows and arrows. Police surrounded the area Sunday night and began moving in after issuing an ultimatum for people to leave the area. The crowd wore raincoats and carried umbrellas to shield themselves.

Riot officers broke in before dawn as fires raged inside and outside the school. As riot police moved in from all sides, some protesters retreated inside the university while others set fires on bridges leading to it.

Police, who have warned that everyone in the area could be charged with rioting, reportedly made a handful of arrests.

WATCH: Volleys of fire bombs, water cannons exchanged outside Hong Kong university

Police deployed water cannons outside Hong Kong's Polytechnic University as protesters hurled gas bombs outside the barricaded campus. 0:57

At daybreak, protesters remained in control of most of the campus. In one outdoor area, some demonstrators made gasoline bombs while others dozed with their gas masks on. Two walked about with bows and quivers of arrows, while many stared at their smartphones.

Jin-Guang Teng, the president of Hong Kong Polytechnic University, later said that police have agreed to suspend their use of force. Teng added that police would allow protesters to leave the campus, and that he would accompany them to the police station to ensure that their cases "will be fairly processed."

He said in a recorded video message that he hopes protesters "will accept the proposed temporary suspension of force and leave the campus in a peaceful manner." It seems unlikely the protesters would accept the offer given that they would all likely be arrested.

As dozens of protesters streamed out of the campus, police used tear gas to drive them back. They likely wanted to try to escape, while police want to arrest them.

Protesters jump back inside Hong Kong Polytechnic University after police used tear gas as they were trying to leave. (Adnan Abidi/Reuters)

Live bullets threatened

Earlier, Hong Kong police threatened to respond with live bullets if "rioters" use lethal weapons and commit other acts of violence.

Police issued the statement on Monday, urging people they described as rioters to stop using lethal weapons to attack officers, adding that police would respond with force and could use bullets if they did not comply.

The warning came after a day protesters set fire to bridges leading to Hong Kong's Polytechnic University as they tried to keep police from advancing on their stronghold.

A makeshift barricade of chairs and other debris is seen on a stairway at Hong Kong Polytechnic University. (Adnan Abidi/Reuters)

There were flames on the length of a footbridge over the roadway entrance to the Cross-Harbour Tunnel, just south of the university. Police had shut access to the area and massed earlier in an apparent attempt to surround protesters. Some retreated inside the campus while others remained outside to deter any advance.

Another fire was set on a bridge over the toll booths for the tunnel. Protesters have blocked access to the tunnel for days and set fires in the toll booths.

Several protesters fired arrows from the rooftops of the university amid some of the most dramatic scenes in over five months of unrest in the Chinese-ruled city.

Officer hit by arrow

Police said a media liaison officer was hit in the leg by an arrow. He was taken to hospital for treatment. A metal ball hit another officer in the visor, but he was not wounded.

Protesters, concerned about the contents of blue liquid that police fired from water cannons, stripped down to their underwear before being hosed down by colleagues with fresh water.

An anti-government protester uses a bow during clashes with police outside Hong Kong Polytechnic University in Hong Kong on Sunday. (Athit Perawongmetha/Reuters )

Police also fired tear gas to try to break up protesters on the artery of Nathan Road in the Kowloon district of Mong Kok, a frequent venue for unrest.

Huge fires had lit up the sky at the university in the heart of Kowloon district overnight as protesters hurled gasoline bombs, some by catapult, and police fired volleys of tear gas to draw them on to the open podium of the red brick campus.

Water cannon and gasoline bombs

The clashes spread into Sunday evening, with protesters greeting each water cannon charge with gasoline bombs.

"Rioters continue to launch hard objects and petrol bombs with large catapults at police officers," police said in a statement. "The shooting range of such large catapults can reach up to 40 metres ... Police warn that the violent activities in the Hong Kong Polytechnic University have escalated to rioting."

In the university courtyard, civil engineer Joris, 23, said he would be prepared to go to jail in his fight against the government. Those shooting arrows were protecting themselves, he said.

Protesters clash with police as police fire teargas at them at the Hong Kong Poytechnic University on Sunday. (Anthony Kwan/Getty Images)

"The police violence has been over the top," he told Reuters. "The protesters have been reacting to the police. We haven't fought back as much as we could. I would be prepared for jail. We are fighting for Hong Kong."

Reuters correspondents heard a high-pitched wailing coming from at least one police vehicle, suggesting a new weapon in their crowd dispersal arsenal.

Chinese soldiers in a base close to the university were seen monitoring developments with binoculars, some dressed in riot gear with canisters on their chests.

Chinese soldiers dressed in shorts and T-shirts, some carrying red plastic buckets or brooms, emerged from their barracks on Saturday in a rare public appearance to help residents clear debris blocking key roads.

'We are not afraid'

Parts of the Hong Kong Polytechnic University campus looked more like a fortress with barricades and black-clad protesters manning the ramparts with improvised weapons-like bricks, crates of fire bombs, and bows and arrows at the ready.

"We are not afraid," said a year-three student Ah Long, who chose not to disclose his full name. "If we don't persist, we will fail. So why not (go) all in," he said.

A protester runs after throwing a molotov cocktail at the police outside the Hong Kong Polytechnic University. (Ye Aung Thu/AFP via Getty Images)

The campus is the last of five universities to remain occupied, with activists using it as a base to continue to block the city's central Cross-Harbour Tunnel.

The presence of China's People's Liberation Army (PLA) soldiers on the streets, even to help clean up, could stoke further controversy over Hong Kong's autonomous status at a time many fear Beijing is tightening its grip on the city.

The Asian financial hub has been rocked by months of demonstrations, with many people angry at perceived Communist Party meddling in the former British colony, which was guaranteed its freedoms when it returned to Chinese rule in 1997.

Beijing denies interfering and has blamed the unrest on foreign influences.

Clashes between protesters and police have become increasingly violent, posing the gravest popular challenge to Chinese President Xi Jinping since he came to power in 2012.

WATCH: Hong Kong protesters hurl gas bombs at police:

Clashes between protesters and police have turned violent at times in Hong Kong, which is grappling with its biggest political crisis in decades. 0:56

Xi has said he is confident the Hong Kong government can resolve the crisis. Until Saturday, Chinese troops in the city had remained inside their base during the protests.

Chinese troops have appeared on Hong Kong's streets only once since 1997, to help clear up after a typhoon in 2018.