China said Hong Kong’s protest movement had reached “near terrorism” on Wednesday, after a night of ugly clashes at the city’s airport where demonstrators set upon and detained two men they suspected of being government sympathisers.

Flights out of the financial hub resumed after two days of disruptions caused by unrest as thousands of protesters swarmed the terminal at one of the world’s busiest airports, forcing the cancellation of hundreds of departures.

China’s Hong Kong and Macau Affairs Office in Beijing called the behaviour at the airport no different to terrorism and said it must be severely punished.

Ten weeks of increasingly violent clashes between police and protesters have plunged the city into its worst crisis since it reverted from British to Chinese rule in 1997.

“We’re deeply sorry about what happened yesterday,” read a banner held up by a group of a few dozen demonstrators in the airport arrivals hall. “We were desperate and we made imperfect decisions. Please accept our apologies,” the banner said.

In chaotic scenes that would once have been unthinkable for Hong Kongers, a peaceful sit-in at the airport turned violent late on Tuesday as protesters confronted and held a man they believed was an undercover Chinese agent.

Busloads of riot police arrived in response, clashing with demonstrators before withdrawing once the man was removed and leaving the terminal briefly in control of activists who then detained a Chinese reporter.

Protesters, who occupied the airport for five days — disrupting flights on Monday and Tuesday — mostly withdrew by daybreak, with several groups issuing statements blending contrition for the chaos with defiance of the authorities.

It’s not clear whether the ugly scenes have eroded the broad support the movement has attracted in Hong Kong, while the city’s faltering economy has also taken a hit in recent months.

“We promise to reflect and to improve,” protesters said in one message distributed on social-media app Telegram.

“Sorry we were too reckless ... we are only afraid of losing your support to the whole movement due to our mistake, and that you give up on fighting.”

The unrest began in opposition to a now-suspended bill that would have allowed the extradition of suspects for trial in mainland China, but have swelled into wider calls for democracy.

The seizure by protesters of a reporter from China’s Global Times newspaper, a nationalistic tabloid run by the ruling Communist Party’s official People’s Daily, and their harassment of the man they believed to be a mainland agent drew China’s strongest language yet.

In addition to Beijing’s condemnation, the People’s Daily called for “using the sword of the law” to restore order, and mainland social media users lauded the detained reporter as a hero.

On Tuesday, US President Donald Trump described the volatile situation as “tricky”, and said China’s government had moved troops near the border with Hong Kong.

“I think it will work out and I hope it works out, for liberty. I hope it works out for everybody, including China,” he told reporters during a visit to Morristown, New Jersey.

Chinese police have assembled in the neighbouring city of Shenzhen for what appeared to be exercises, the Global Times reported this week. China also denied a request for two US Navy warships to visit Hong Kong in the coming weeks, US officials said.