Some of the protesters who had been occupying the airport's arrivals hall swarmed into the departures area on Monday, prompting authorities to cancel all flights and advise travellers to leave one of the world's busiest hubs.
The action came in response to a sharp increase in the level of force employed by Hong Kong's embattled police.
Hours before the airport shutdown, two police officers elsewhere in the city had pinned a black-clad demonstrator to the concrete, one officer's knee pressing the young man's face into a pool of his own blood.
"I've already been arrested," the man yelled as he cried for help. "Don't do this, I'm begging you."
The scene, captured Sunday night by a cameraman from the Hong Kong Free Press, was jarring even in a city now accustomed to weekends awash with tear gas. It unleashed a fresh wave of anger toward Hong Kong's police force, and the government more broadly, spurring thousands of demonstrators to respond by occupying the airport.
Meanwhile, fears mounted that Beijing would soon resort to military action to quell the protests in the semiautonomous territory.
The nationalist Global Times tabloid tweeted a video showing Chinese armoured personnel carriers heading toward the southern city of Shenzhen, which borders Hong Kong, ahead of what the paper called "large-scale exercises" by the People's Armed Police, a paramilitary unit.
In the accompanying story, the newspaper elaborated: "The tasks and missions of the Armed Police include participating in dealing with rebellions, riots, serious violent and illegal incidents, terrorist attacks and other social security incidents."
China's state broadcaster, CCTV, issued a commentary Monday night headlined: "Alert! There are signs of terrorism on the streets of Hong Kong."
It warned: "No country can accept terrorist acts in its own country. . . . Hong Kong has reached an important juncture. 'End violence and restore order' is the most important, urgent and overriding task of Hong Kong at present!"