Hong Kong police and protesters clashed at the Hong Kong International Airport on Tuesday evening.

Earlier the airport reopened after cancelling all flights on Monday, only to cancel flights again on Tuesday due to the protests.

Airport Authority said operations had been “seriously disrupted” on Tuesday and departing passengers had been unable to reach immigration counters.

In a second day of unrest at the airport, thousands of protesters dressed in black filled the terminal, chanting, singing and waving banners.

Scuffles broke out after an injured person was taken out of the main terminal by medics after he was held by a group of protesters. Some activists claimed he was an undercover mainland Chinese police officer.

Several police vehicles were blocked by protesters and riot police moved in, pushing some protesters back and using pepper spray. A policeman pulled out a gun at one point.

Protesters also barricaded some passageways in the airport with luggage trolleys, metal barriers and other objects. At least two protesters were taken away by police.

The situation calmed down after a few hours without the violence worsening.

The weeks of protests began as opposition to a now-suspended bill that would have allowed suspects to be extradited to mainland China and have swelled into wider calls for democracy.

Demonstrators say they are fighting the erosion of the “one country, two systems” arrangement that enshrined some autonomy for Hong Kong since China took it back from Britain in 1997.

Ten weeks of increasingly violent clashes between police and protesters have roiled the Asian financial hub. Hong Kong’s stock market fell to a seven-month low on Tuesday.

The United Nations human rights commissioner, Michele Bachelet, urged Hong Kong authorities to exercise restraint and investigate evidence of their forces firing tear gas at protesters in ways banned under international law.

In response, China said her comments sent the wrong signal to “violent criminal offenders”.

Chief Executive Carrie Lam made an appeal for calm and restraint.

“Take a minute to look at our city, our home,” she said, her voice cracking, at a news conference in the newly-fortified government headquarters complex.

“Can we bear to push it into the abyss and see it smashed to pieces?” she said.

Protesters are demanding for the resignation of MS Lam but she maintains she’ll stay.

Despite the trouble, some flights were still scheduled to take off early on Wednesday morning with some tourists still waiting in the departure hall and dining areas, according to Reuters.

Meanwhile, China’s civil aviation regulator demanded that the airline suspend staff who joined or backed the protests from flights in its airspace, pushing the carrier’s shares past Monday’s 10-year low.