Over the weekend, the site had been used to stockpile weapons, including bows and arrows, catapults and petrol bombs, though it was unclear how many weapons remained.

Earlier Monday morning, the president of the university's student union said in a statement posted to Facebook that "thousands" of students were still on the campus, some of whom were injured. "We have tried to communicate with school authorities, but we have not received any reply after more than two hours," the president Derek Liu said.

Liu accused riot police of storming the collegiate area of the university and carrying out "a massive arrest" of protesters. In a statement, police said claims that police "raided" the university were "totally false."

Images from the ground on Monday morning showed scenes of devastation around the campus, with debris and trash littering nearby streets.

Schools are closed across the city on Monday, extending a disruption that began last week. In a statement on Sunday, the government said the closures were "for the sake of safety."

University 'widely damaged'

Police attempted to clear the roads around Polytechnic University on Saturday night but were forced to back down after protesters started fires on the street and threw petrol bombs and bricks using catapults. Their hold on the high ground made it difficult for police vehicles to advance.

"They showed total disregard for the safety of everyone at scene," police said in a statement Sunday, confirming they tried to disperse the group using tear gas.

A 23-year-old protester and Polytechnic University alumnus told CNN on Sunday he didn't have a plan and was just waiting to see how the police would react. "If we don't come out, no one will come out and protect our freedoms. Polytechnic University is my home," he said.

Protesters on Sunday were using catapults to launch bricks and other hard objects at police lines from the university's balconies.

"Such attacks pose a grave threat to the safety of police officers, reporters and first aiders at the scene," said police in a statement, accusing protesters of firing petrol bombs and metal balls at their lines.

On Sunday, the management of Hong Kong Polytechnic University issued a statement saying "dangerous chemicals" had been stolen from laboratories and condemned the protesters' "illegal acts and violence" in the campus which has, they say, "been widely damaged."

"We understand that students care about the current social situation, however, they must be calm and rational when fighting for anything," the statement said. "Resorting to violence or other radical acts will not help solve the problem."

In a fiercely worded statement, the police labeled the group holding the university "rioters," a loaded term in Hong Kong's protests that could result in a heavy prison sentence.

In a statement Sunday evening, the Hong Kong Professional Teachers' Union and the university's Staff Association said they were "very worried" about the safety of students and bystanders.

"We call on both sides to exercise restraint and avoid the use of deadly weapons. The current stalemate is caused by a series of government decision-making mistakes and should be resolved responsibly," the statement said.

Six months of chaos

When the government suspended but didn't withdraw the bill, the movement's focus quickly expanded to focus on complaints of police brutality and wider calls for democracy.

With both the government and protesters refusing to back down, there is no immediate end in sight to the Hong Kong demonstrations.

He said that "radical" protesters had trampled the city's rule of law and that "stopping the violence and restoring order" was Hong Kong's most "urgent task."

It came just hours before a 70-year-old man, who was struck by a brick during clashes between protesters and their opponents, died of his injuries. Police blamed protesters for throwing the object that killed him.

Even that incursion was enough to spur pro-democracy lawmakers in Hong Kong to push for an explanation from the city's government.

Chinese soldiers' efforts to clear roadblocks outside their barracks in Kowloon Tong was "purely a voluntary community activity initiated by themselves," the Hong Kong special administrative region government said in a statement to CNN.