Hong Kong authorities have issued an ultimatum to protesters to leave their improvised stronghold at the city's Polytechnic University, with riot police moving on a group of protesters on Sunday evening.

Some 200 protesters, most of them believed to be students, remain inside the university. Police gave them one exit route to leave the area. The protesters appeared undaunted by the ultimatum, lighting fires on bridges leading to the campus and reportedly setting the entrance on fire amid police attempts to enter the building.

Previously, a police officer was shot in the leg with an arrow during an earlier clash with a group of Beijing critics near the Kowloon campus.

Hong Kong police released images of the police liaison officer's lower leg with an arrow in it.

Police spokesman Louis Lau said that police might open fire if protesters continued to use "deadly weapons."

"If they (protesters) continue such dangerous actions, we would have no choice but to use minimum force, including live rounds," Lau said during a Facebook live broadcast.

Protesters have used bows and arrows several times over the past week, but this marked the first time an officer was hit. Three protesters have so far been shot by the police in the crisis, which has now lasted several months.

"Rioters continue to launch hard objects and petrol bombs at police officers with large catapults," Hong Kong's police force said in a statement.

The police stated that the activities at the university had "escalated to rioting."

Activists had set fires on footbridges leading up to the university and launched petrol bombs at police who tried to gain access to the building. They continued to block the main tunnel connecting Kowloon to Hong Kong Island that protesters have managed to hold for days.

Violence also flared up at the nearby Cross-Harbour Tunnel on Saturday night and throughout Sunday.

Wong defends protesters

On Sunday, several hundred people formed a human chain in central Hong Kong in a peaceful show of support for the movement.

Hong Kong activist Joshua Wong defended the protesters' stance while talking to German media.

"We will not achieve our goal with purely peaceful protest," he told the German daily Süddeutsche Zeitung. "And we will not achieve it with violence alone. We need both," he was quoted as saying in the German-language article.

Wong also said that over 4,000 people have been arrested since the protest started.

Confrontation between rival groups 

The protesters also faced off with a large group of government supporters who attempted to clear barricades and remove debris from a roadway near the campus.

Read more: Hong Kong: 'For the protesters, this is a kind of endgame'

Protesters occupied several major Hong Kong universities last week, but the Polytechnic is believed to be the only one they still hold.

A message on the university's Facebook page called on protesters to leave immediately.

"In view of safety concerns posed by possible violent unlawful activities conducted by protesters who are still occupying the PolyU campus, the University again urges all people on campus, including students and staff members, not to stay, and to leave as soon as possible," the post read.

PLA on the streets

On Saturday, squads of Chinese People's Liberation Army soldiers joined residents in cleaning up debris.

Opposition lawmakers criticized their appearance on the streets, warning that it could be seen as an attempt to interfere in local affairs. 

Read more: Hong Kong: Protesters leave university campus and barricade highway

The unrest has brought much of the financial hub to a standstill, shutting down the train network, and forcing the closure of schools and businesses.

The protests were triggered by a proposed law allowing for the extradition of criminal suspects to mainland China. Although the bill was ultimately dropped, the protests have expanded into a wider resistance movement demanding full democracy. 

The legislation was seen by many in Hong Kong as an attempt by Beijing to erode the autonomy the territory was guaranteed when Britain handed it over to China in 1997.

dj,kmm,nm/bk (AP, Reuters, AFP)

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