An official in Beijing on Tuesday issued China’s sternest denunciation yet of the demonstrations in Hong Kong, saying they had “exceeded the scope of free assembly” and warning that the semiautonomous city would not be allowed to descend into chaos.

“I want to warn all the criminals to not wrongly judge the situation and take restraint for weakness,” said Yang Guang, a spokesman for the Chinese government’s Hong Kong and Macau Affairs Office. He warned against underestimating China’s “firm resolve and strength to safeguard the prosperity and stability of Hong Kong.”

But Yang offered little in the way of concrete measures to resolve the political crisis, calling for more patriotic education and encouraging residents to confront protesters. “We need to stand up to protect our wonderful homeland,” he said.

The comments came a day after protesters in Hong Kong carried out their most widespread civil disobedience in weeks of demonstrations, blocking trains and roads and urging workers to strike. Air travel was also snarled, with more than 200 flights cancelled after 2,300 civil aviation workers stayed home, according to an estimate by union officials.

Yang denounced the tactics of protesters who have surrounded police stations, throwing bricks and lighting fires, as “extreme violence that is shocking to see”.

He said, “The central government will never allow any violent attempt to push Hong Kong into a dangerous situation.”

Protesters gathered at more than a half dozen sites across Hong Kong on Monday, and the police arrested 148 people and fired 800 canisters of tear gas. The tear gas used on Monday alone came close to the 1,000 rounds that the police had used over the previous eight weeks.

Joshua Wong, a leader of the 2014 Umbrella movement and a prominent pro-democracy activist in Hong Kong, said Yang’s comments were an attempt to scare the people of the city into silence.

“Beijing does not rule Hong Kong by law, they just rule by tear gas,” he said.

The protests this summer began over a proposal that would have allowed extraditions to mainland China. The government suspended that legislation in mid-June, but the protests have continued, demanding that the government fully withdraw the bill.

The protesters are also angry about other issues, including allegations of police brutality and the stalled expansion of direct elections in Hong Kong.

Protesters who have clashed with the police have argued that more confrontational methods became necessary after the government rejected demands made in earlier, peaceful marches, one of which was joined by as many as two million people.

Yang also warned protesters to not challenge China’s sovereignty, denouncing those who defaced the Chinese government’s representative office in Hong Kong last month and threw Chinese flags into Victoria Harbor in recent days. He criticised protesters’ use of a slogan from an imprisoned activist who once advocated Hong Kong’s independence: “Liberate Hong Kong; revolution of our times.”

Last week, the Hong Kong and Macau Affairs Office expressed its support for Carrie Lam, the Hong Kong chief executive, but they offered little new to resolve the political crisis. It was rare for the office to hold a news conference, and even rarer for it to hold another just a week later.