Flights leaving Hong Kong were disrupted for a second day on Tuesday, plunging the former British colony deeper into turmoil as its stockmarket fell to a seven-month low, and its leader said it had been pushed into a state of "panic and chaos".

The United Nations High Commissioner for Human Rights also urged Hong Kong to exercise restraint and investigate evidence of its forces firing tear gas at protesters in ways banned under international law.

Ten weeks of increasingly violent clashes between police and protesters have roiled the Asian financial hub as thousands of residents chafe at a perceived erosion of freedoms and autonomy under Chinese rule.

China this week condemned some protesters for using dangerous tools to attack police, calling the clashes "sprouts of terrorism" despite images of peaceful sit-ins, including protesters singing music from the musical "Les Miserables" going viral around the world. The protests present President Xi Jinping with one of his biggest challenges since he came to power in 2012.

Hong Kong legal experts say Beijing might be paving the way to use anti-terror laws to try to quell the demonstrations. Chinese state media outlets warned on Tuesday that protesters in Hong Kong are “asking for self-destruction,” as they released a video showing military vehicles amassing near the border of the city.

Check-in operations were suspended at 4.30 p.m. on Tuesday, a day after an unprecedented airport shutdown, as thousands of black-clad protesters jammed the terminal, chanting, singing and waving banners.

"Take a minute to look at our city, our home," Chief Executive Carrie Lam said, her voice cracking, at a news conference in the government headquarters complex, which is fortified behind 6-foot (1.8-m) -high water-filled barricades.

"Can we bear to push it into the abyss and see it smashed to pieces?"

The protests began as opposition to a now-suspended bill that would have allowed suspects' extradition to mainland China, but have swelled into wider calls for democracy.

At the airport, thousands of protesters gathered in the arrivals hall, as well as some parts of departures, using luggage trolleys to blockade the doors to customs checkpoints.

Floors and walls were covered with missives penned by activists and other artwork. The scene was peaceful as knots of protesters spoke to travellers, explaining their aims.

"Sorry for the inconvenience, we are fighting for the future of our home," read one protest banner at the airport.

"I think paralysing the airport will be effective in forcing Carrie Lam to respond to us ... it can further pressure Hong Kong's economy," said Dorothy Cheng, 17.

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.

They want Lam to resign. She says she will stay.

"My responsibility goes beyond this particular range of protest," she said, adding that violence had pushed the territory into a state of "panic and chaos".

As she spoke, the benchmark Hang Seng index hit a seven-month low. It shed more than 2%, dragging down markets across Asia.

Lam did not respond to questions at a press briefing to clarify if she had the power to withdraw the extradition bill and satisfy a key demand made by the protesters, or if she needed Beijing's approval.

AIRPORT DISRUPTED

Airport authorities had earlier suspended check-in operations as the fifth day of a sit-in by protesters grew increasingly heated. Crowds continued to swell in the evening.

"Terminal operations at Hong Kong International Airport have been seriously disrupted as a result of the public assembly," the airport authority said.

Some passengers challenged protesters over the delays as tempers began to fray, while the demonstrators, using a Chinese term of encouragement, chanted, "Hong Kong people - add oil!"

Flag carrier Cathay Pacific warned: "There is potential for further flight disruptions at short notice."

The airline, whose British heritage makes it a symbol of Hong Kong's colonial past, is also in a political bind.

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.

Other Chinese airlines have offered passengers wanting to avoid Hong Kong a free switch to nearby destinations, such as Guangzhou, Macau, Shenzhen or Zhuhai, with the disruption sending shares in Shenzhen Airport Co Ltd surging.

On Monday China said the protests had reached a critical juncture, after a weekend of street clashes in which both police and protesters appeared to toughen their resolve.

Police fired tear gas at the blackshirted crowds in districts on Hong Kong island, Kowloon and the New Territories.