- The decision came after thousands of pro-democracy protesters flooded into the airport for the second consecutive day and blocked passengers from reaching entrances to the departure area in both terminals.
Hundreds of flights were cancelled or suspended at Hong Kong's airport on Tuesday as pro-democracy protesters staged a second day of hugely disruptive rallies, defying warnings from the city's leader who said they were heading down a "path of no return".
The new protest came as Beijing also sent further ominous signals that the 10 weeks of unrest must end, with state-run media showing videos of security forces gathering across the border.
The crisis, which has seen millions of people take to Hong Kong's streets, was before this week already the biggest challenge to Chinese rule of the semi-autonomous city since its 1997 handover from Britain.
But the two days of protests at the airport, one of the busiest in the world, raised the stakes yet again.
All check-ins were cancelled on Tuesday afternoon after thousands of protesters wearing their signature black T-shirts made barricades using luggage trolleys to prevent passengers from passing through security gates.
"I want to shut down the airport just like yesterday so most of the departure flights will be cancelled," a 21-year-old student who gave his surname as Kwok told AFP.
On Monday a crowd that police said numbered 5,000 filled the building to denounce what they said were violent tactics by police in trying to quell weekend rallies.
Airport authorities in response cancelled all flights on Monday afternoon.
On Tuesday morning, the city's leader, Carrie Lam, gave an at-times emotional press conference in which she warned of dangerous consequences if escalating violence was not curbed.
"Violence, no matter if it's using violence or condoning violence, will push Hong Kong down a path of no return," Lam said.
"The situation in Hong Kong in the past week has made me very worried that we have reached this dangerous situation."
Lam, who faced fierce questioning from local reporters and at one point appeared to be on the verge of tears, appealed for calm.
"Take a minute to think, look at our city, our home, do you all really want to see it pushed into an abyss," Lam said, although she again refused to make any concessions to the protesters.