Video report by ITV News International Affairs Editor Rageh Omaar
Violent clashes have broken out at Hong Kong airport after riot police stormed the terminal to disperse protesters.
Officers charged on pro-democracy campaigners, arresting people staging a sit-in at one of the world's busiest airports.
The airport has been forced to cancel more than 300 flights on the second day of disruption - coming after more than 200 planes were grounded on Monday.
A police officer also drew his firearm as protesters backed him up against an airport terminal window - the moment was caught on camera by freelance journalist Michael Zhang.
Emergency services have also taken an injured mainland Chinese man away from the airport after angry protesters who accused him of being a Chinese undercover agent tied up his hands and tried to beat him up.
US President Donald Trump tweeted "everyone should be calm and safe" after his intelligence services reported to him that Beijing was moving troops to the border.
Hong Kong's leadership had earlier warned pro-democracy protesters not to push the city into an "abyss".
But critics hit back at chief executive Carrie Lam during a press conference, heckling after she dodged a question on the policing of protests.
The disruption follows the airport, one of the busiest in the world, being forced to halt planes on Monday, cancelling more than 200 flights.
Protesters remain in airport terminal demanding resignations
Throughout Tuesday, protesters showed no sign of letting up on their campaign to force Ms Lam’s administration to respond to their demands.
Initially, the demonstrations began after Hong Kong's government attempted to introduce an extradition bill which would mean criminal suspects could face trial in mainland China.
Following the bill's unpopularity, Ms Lam has said it had been suspended and was "dead".
Since then, the demonstrations have morphed to include calls Ms Lam's resignation, democratic elections in the semi-autonomous Chinese territory, the release of those arrested in earlier protests and an investigation into police use of force against the protesters.
Earlier on Tuesday, in a press conference in which she at times appeared close to tears, Ms Lam told reporters dialogue would only begin when the violence stopped.
She reiterated her support for the police and said they have had to make on-the-spot decisions under difficult circumstances, using "the lowest level of force".
"After the violence has been stopped, and the chaotic situation that we are seeing could subside," she said, "I, as the chief executive, will be responsible to rebuild Hong Kong’s economy… to help Hong Kong to move on."
The 62-year-old did not elaborate on what steps her government will take toward reconciliation.
After two months, the protests have become increasingly divisive and prompted clashes across the city.
Passengers frustrated by lack of departures
Software engineer Joydeep Chakravarti, whose connecting flight to San Francisco was cancelled late on Monday, was among those caught up in disruption following the protests and expressed frustration that he was told to leave the airport when he wanted to stay inside the terminal.
“I don’t know what’s out there, so I don’t want to leave.
"I didn’t make any plans for Hong Kong,” said Mr Chakravarti, who had a carry-on bag with laptop, charger and an extra shirt, while the rest of his luggage was already checked in on his Singapore Airlines flight.
The protests have seen clashes between both sides, and on Sunday, police fired tear gas into Kwai Fong station.
A number of people were reportedly hurt in Sunday's clashes, including a woman who was said to have been blinded after allegedly being fired at by police.
Protesters at the airport wore eye patches as a marker of the violence.
Hong Kong was promised certain democratic rights when China took over the then-British colony in 1997, but in recent years, some have accused Beijing of steadily eroding their freedoms.