Hong Kong authorities urged radical protesters who have fortified themselves in a campus to come out and surrender to police.

The calls were made after a day of fiery clashes at the Hong Kong Polytechnic University that started on Sunday afternoon, making it one of the most violent days since protests broke out in June.

Radical protesters trapped inside the campus should follow police instructions to leave in a peaceful manner, Chief Secretary Matthew Cheung Kin-chung said at a news conference on Monday.

He condemned some rioters who, in utter disregard of public safety, repeatedly charged at police cordons by using deadly weapons, including arrows and gasoline bombs.

The radicals will be arrested on suspicion of rioting, an offense that carries up to 10 years in prison, when they drop their weapons and walk out of the campus, according to Cheuk Hau-yip, regional commander of Kowloon West of the Hong Kong Police Force. There is no other viable option for them, Cheuk said.

The police had earlier arrested a number of protesters who were trying to flee by pretending to be first-aid providers or journalists.

Secretary for Security John Lee Ka-chiu also confirmed no force will be used if protesters surrender peacefully.

The university campus is still full of dangerous objects, including explosives and corrosive liquids, Lee noted.

The police have sent Red Cross volunteers, Social Welfare Department officers and government psychologists into the campus to help the injured and underage protesters.

Radicals clashed with police on Monday at noon as they tried to escape the campus. Some 100 of them managed to abscond after dark by rappelling down to a highway where they were picked up by motorcycle drivers. Fires raged again on the campus amid sounds of explosions, while supporters of the radicals flooded major thoroughfares in Kowloon as they marched toward PolyU. Train services were also disrupted.

The prolonged standoff near the university has seen a police armored vehicle set ablaze, an officer shot in his leg by an arrow, and police fire a live round at a car ramming into the police line amid intensive rounds of gasoline bombs and tear gas.

On Monday, police confirmed that three universities — PolyU, the Chinese University of Hong Kong and City University of Hong Kong — had reported dangerous chemicals such as flammable, toxic and corrosive substances missing after radicals stormed their laboratories.

Police arrested 154 people in connection with violent demonstrations during the past weekend. A total of 4,491 people have been arrested since protest violence broke out in June.