Flight check-in has been suspended at Hong Kong International Airport for a second consecutive day because of anti-government protests.
The airport, which is one of the world’s busiest, has been the site of daily protests since Friday.
Despite the latest warnings from officials, crowds gathered at the airport again on Tuesday.
Images from inside appeared to show protesters using luggage trolleys to build barriers and some travellers becoming distressed and angered at the disruption.
Videos on social media showed passengers struggling to get through demonstrators, who were sitting inside and blocking departures.
Amid tense scenes, police and protesters clashed outside the airport.
The police, wearing riot gear and brandishing truncheons, are said to have deployed pepper spray to push protesters back.
In an ugly incident, young protesters mobbed a man they suspected was an undercover policeman and zip-tied his hands together. Paramedics struggled to treat the man amid a crowd of angry protesters before he was taken to hospital.
The editor of China’s Global Times newspaper said the man was one of his reporters who was merely doing his job.
Hong Kong police have admitted deploying officers disguised as anti-government protesters during the unrest in the city.
The city’s leader, Carrie Lam, earlier issued a fresh warning to protesters.
Lam said Hong Kong had “reached [a] dangerous situation” and that violence during protests would push it “down a path of no return”.
President Donald Trump of the United States said on Twitter that US intelligence had informed him of a deployment of “troops” to Hong Kong by China.
“Our Intelligence has informed us that the Chinese Government is moving troops to the Border with Hong Kong. Everyone should be calm and safe!” President Trump tweeted.
Mass unrest has rocked Hong Kong for 10 weeks and shows no signs of abating.