HONG KONG — Bearing batons and pepper spray, Hong Kong riot police officers clashed with anti-government protesters who crippled the airport on Tuesday for the second straight day, chaos that underscored the deepening unrest gripping the city.
The mayhem at the airport — in the Asian financial hub known for efficiency and order — came hours after mass protests forced the airport to suspend check-ins, as it had done on Monday. The city’s embattled leader, Carrie Lam, had pleaded earlier for order after days of escalating street violence.
Thousands of demonstrators had occupied parts of Hong Kong International Airport’s departures and arrivals halls on Tuesday afternoon, with some using luggage trolleys to block travelers from reaching their departure gates. The Hong Kong Airport Authority later closed check-in services and advised all passengers to leave as soon as possible.
As of early Tuesday evening, some arriving flights were still scheduled, along with some departures, apparently for passengers who had managed to clear immigration before check-in closed. But Cathay Pacific Airways, Hong Kong’s flag carrier, told its customers to postpone “nonessential travel” out of the city for the rest of the day and on Wednesday.
Monday was the first day that demonstrators had seriously disrupted operations at the airport, one of the world’s busiest. The escalation of the protests is another sign that the two-month-old movement is turning to increasingly desperate measures, amid threats from Beijing and the refusal of Mrs. Lam, Hong Kong’s chief executive, to meet their demands.
Hong Kong is facing its worst political crisis since the former British colony returned to Chinese rule in 1997 as a semiautonomous territory. The intensifying unrest this month has stoked widespread anxiety in the financial hub, in part because Beijing has started to warn protesters in increasingly strident terms to stand down or face consequences.
President Trump on Tuesday weighed in via tweet, saying “our intelligence has informed us that the Chinese Government is moving troops to the border with Hong Kong.”
It’s unclear what information, if any, Mr. Trump has. While Chinese security forces have conducted large-scale operations across the border from Hong Kong in Shenzen in recent days, they appear to mainly be a nationalistic show of force.
The clashes at the airport began late in the evening when police vans arrived outside the departures hall, which was full of black-clad protesters.
Some of the protesters went outside, blocked the vans with makeshift blockades and threw plastic bottles at them. At one point, some officers in riot gear began running after protesters who were outside the terminal, wrestling some to the ground with batons.
A group of protesters surrounded a police officer inside the terminal. They took his baton and beat him with it, retreating after he appeared to pull a gun.
With tensions running high at the airport late Tuesday, a group of demonstrators surrounded and attacked a man they accused of being a mainland Chinese police officer impersonating a protester, causing him to faint. His identity could not be immediately confirmed.
As midnight neared, bands of black-clad protesters were still in the airport, while bewildered travelers, fresh off arriving flights, walked past them and into the sweltering night. The protest crowd later thinned, as did the police presence.
The continued disruptions at the airport on Tuesday left some travelers frustrated and angry. Some described themselves as supporters of the protest movement who had grown disillusioned with it.
Maisa Sodebayashi, who is from Brazil and works in a car factory in Japan, said that while she understood the protesters were fighting for democracy, she also wanted to catch her flight to Rio de Janeiro. She had been stranded in the airport for about 24 hours.
“Honestly, I don’t know what to do,” Ms. Sodebayashi said, standing beside a customer service desk.
The protesters at the airport have been particularly angered by the tactics used by the police against demonstrators on Sunday, including firing tear gas into a train station and sending officers into crowds dressed as demonstrators to make arrests.
On Tuesday, the United Nations’ human rights chief, Michelle Bachelet, said there was evidence that the Hong Kong police had violated international standards for the use of less-lethal weapons like tear gas.
In a news conference with combative reporters on Tuesday morning, Hong Kong’s leader, Mrs. Lam, urged protesters to obey the law.
“The stability and well-being of seven million people are in jeopardy,” Mrs. Lam said, her voice breaking slightly. “Take a minute to think about that. Look at our city, our home. Do we really want to push our home to the abyss where it will be smashed into pieces?”
During street clashes this summer, the Hong Kong police have regularly fired tear gas, rubber bullets and bean bag rounds to disperse protesters, even in residential areas and crowded shopping districts. On Sunday night, in addition to using tear gas in a train station, the police beat protesters and chased some down an escalator at another station.
The authorities, for their part, accused protesters of attacking officers with bricks and gasoline bombs.
On Tuesday, Mrs. Lam was frequently interrupted by journalists who demanded an explanation for what protesters have called blatant police misconduct. She looked more visibly emotional than she has at other recent public appearances.
“Will you apologize to the girl?” one reporter asked, referring to a woman who was hit in her right eye on Sunday, by a projectile during the city’s 10th straight weekend of mass demonstrations.
“Why have you never condemned the police?” another asked.
Toward the end of the briefing, Mrs. Lam said that police operations were not determined by “someone like myself, who is outside the police.”
Also on Tuesday, medical professionals held rallies at several local hospitals against the police’s tactics and in solidarity with the woman who was hit in the eye on Sunday. The Hong Kong newspaper Apple Daily reported that the injured woman is a veterinary nurse.
The rallies are a “direct response to what happened on Sunday,” Dr. Alfred Wong, a cardiologist who works at Tuen Mun hospital in northwest Hong Kong, said at a gathering there that drew several hundred of his colleagues.
The wave of protests began in early June, in opposition to legislation that would have allowed extraditions to mainland China, where the courts are controlled by the Communist Party.
They have since morphed into calls for more direct elections, a call for Mrs. Lam to resign and an investigation of the police, among other demands.
Beijing, which views the unrest as a direct challenge to its authority, has warned the protesters to stop and has leaned on Hong Kong’s political and business elite to close ranks behind Mrs. Lam, a career civil servant.
Much of the pressure on the business community has focused in recent days on Cathay Pacific, one of the territory’s best-known international brands. The Chinese government has forced it to bar staffers who support or participate in the protests from doing any work involving flights to mainland China.
On Tuesday afternoon, Rupert Hogg, the airline’s chief executive, warned employees against participating in Tuesday’s airport demonstration because it was not sanctioned by the government.
“It is important that you do not support or participate in this protest,” Mr. Hogg said in an internal email. “Again, we would be concerned about your safety if this protest becomes disorderly or violent.” Cathay also said on Tuesday that it had suspended an officer for misusing company information the day before.
As if to eliminate any possible ambiguity about the airline’s stance on the unrest, Cathay’s largest shareholder, the Hong Kong-based conglomerate Swire Pacific, issued a statement on Tuesday condemning “all illegal activities and violent behavior.”
So far, the disruptions have not affected cargo flights in or out of Hong Kong’s airport, which handles more cargo traffic than any other airport in the world. But more and more airfreight is carried nowadays in the bellies of wide-body passenger planes, and these shipments have invariably been disrupted.
Much of the drama at the airport on Tuesday evening centered on confrontations between protesters and what appeared to be two men from the Chinese mainland in the departures hall.
First protesters surrounded the man believed to be a mainland Chinese police officer, pushed him to the ground, and punched and kicked him. He fainted at one point, and medics and police later evacuated him in an ambulance.
Protesters also surrounded another man, bound his hands and feet, searched his belongings and punched him. Some accused him of being a “fake” reporter. He, too, was evacuated in an ambulance.
Hu Xijin, the editor in chief of the Global Times, a nationalist tabloid in the Chinese mainland, wrote in a Twitter post that the man, Fu Guohao, was one of his reporters. “This shows that they have lost their sense of reason,” he later told a New York Times reporter in a message. “Hatred has muddled their minds.”
In television footage of the incident, Mr. Fu can be heard telling his captors with a smile in Mandarin, the primary mainland Chinese dialect, that he supports the Hong Kong police.
“You can beat me up now,” he said.