Hong Kong police defended the decision to raid a university campus on Wednesday, saying they believed the institution was being used as a bomb-making “factory” to target its officers.

Students armed themselves with bows and arrows, javelins and other equipment raided from a sports complex as well as armfuls of petrol bombs, with classes suspended across the city.

There was no sign of a let-up in clashes as the violence entered a third day of the working week, a new development in a months-long crisis that has previously mostly been restricted to evenings and weekends.

As on Monday and Tuesday, more than a thousand masked protesters occupied key streets in the city’s central business district. As city workers looked on during their lunch breaks, police in full riot gear gave a more muscular response than in previous days, clearing barricades and making arrests.

With a senior police officer issuing dire warnings about a city “on the brink of a total breakdown”, the deteriorating situation was for some becoming untenable.

A Danish technical university ordered all its dozens of students attending courses in Hong Kong “to come [home] to Denmark in an orderly fashion”, saying it took the decision after “some of our students have been forced to move from their dormitories because they were put on fire”.

And the authorities used a police boat to evacuate mainland Chinese students from the Chinese University of Hong Kong, at the epicentre of Wednesday’s clashes, after they complained of sustained harassment at the hands of protesters.

The situation is not expected to ease on Thursday, and the education ministry announced that all primary and secondary school classes would be suspended for safety reasons. It had earlier said that parents could decide themselves whether to keep their children at home.

At the Chinese University of Hong Kong, which saw serious and sustained clashes throughout Tuesday night into Wednesday, protesters filmed themselves “practising” with bows and arrows, including firing flaming arrows into the sky.

Police had been criticised for entering the university campus on Tuesday, by some calling it an attack on higher education.

But police spokesman Tse Chun-chung said at a news conference on Wednesday that the decision to do so was taken after riot police guarding a nearby pedestrian bridge came under repeated attack with molotov cocktails.

He questioned how protesters and students could obtain hundreds of gasoline bombs and deploy them quickly in the area, saying it raised strong suspicions that they had been assembled somewhere on campus.

“Rioters' violence reached a very dangerous and even deadly level,” Tse said, using a loaded term for protesters.

He said police would pursue those breaking the law, no matter who “sheltered” them or where they sought refuge. “Nowhere in Hong Kong is lawless land,” he said. “No excuse, no political motives can justify or glorify this madness.”

The authorities said that over the course of Tuesday’s clashes, police fired 1,567 tear gas canisters, 1,312 rubber bullets and 380 beanbag rounds. A total of 142 people were arrested and 10 people were taken to hospital with injuries.

The Chinese University’s student union president, Jacky So, appealed for an injunction from the High Court to ban police from entering the campus without a warrant or the school's approval.