Thousands of black-clad students rallied in central Hong Kong on Monday at the start of a two-week university boycott, piling pressure on the city’s leaders to resolve months of increasingly violent protests that show no signs of easing.

Students have been the backbone of opposition to government plans to allow extraditions to China – a movement that has morphed into wider protests against Hong Kong’s leadership.

Hundreds have been arrested in violent clashes with police. Beijing has labelled the protesters “terrorists” due to their violence, with an editorial by China’s state news agency on Sunday warning that “the end is coming”.

Chinese foreign ministry spokesman Geng Shuang said on Monday that the protests had “gone beyond the scope of freedom of assembly and demonstration”.

“They have evolved into extreme acts of violence, seriously challenging the legal system and social order of Hong Kong,” he told a press conference.

Hong Kong enjoys freedoms unseen on the Chinese mainland under the “one country, two systems” banner that was inherited following the handover from Britain in 1997.

On Monday, as universities reopened after the summer break, thousands of students skipped classes and gathered instead in central Hong Kong.

“Today is the first day of school, but I still want to come out. I don’t think we will miss anything. This is also a form of learning,” a 19-year-old university student named Tommy said.

Earlier Monday, a call for a general strike went largely unheeded – but riot police patrolled some subway stations after protesters briefly disrupted services during rush hour by preventing train doors from closing.

Elsewhere, secondary pupils formed human chains at schools, and nurses carrying placards lined hospital corridors in flash protests to show support for the anti-government movement.

“Hong Kong is our home . . . we are the future of the city and have to take up the responsibility to save it,” said a 17-year-old secondary school student who gave her surname as Wong.

One nurse suggested the protest is doomed because the Hong Kong government will never concede to protester demands.

“But we still have to stand and say something. At least we have shown the world what is happening,” she said, requesting anonymity.

Over the weekend the city witnessed some of the worst civic violence in decades as protesters lobbed bricks and petrol bombs at police, who responded with tear gas, water cannon and baton charges.

On Sunday, at least a dozen flights were cancelled after protesters blocked routes to the airport.

A day earlier hardcore protesters rampaged through the city centre, setting fires and throwing petrol bombs at riot police in defiance of a ban on marching.

Hong Kong’s security minister described protester violence as “on the verge of being out-of-control”.

“I call on the general public to reject violence, keep our society in order and safeguard the rule of law,” John Lee Ka-chiu told reporters.

Mak Chin-ho, an assistant commissioner of police, said 159 people had been arrested between Friday and Sunday, aged from 13 to 58.

“All this pushes Hong Kong to the brink of great danger,” he told a press briefing.

Embattled city leader Carrie Lam has done little to directly address the crisis, save the offer to form a largely derided “platform for dialogue”.

Her removal is one of the key demands made by protesters, who also want the extradition bill to be formally scrapped, and an independent inquiry into alleged police brutality.

The protesters want the city’s leader and all its lawmakers to be directly elected, scrapping the current system that heavily favours certain candidates.

Hong Kong’s reputation as a stable place to do business has been shaken by the protests. Visitor arrivals have plummeted, hotel vacancies have soared and retailers have reported huge losses.