Riot police stormed Hong Kong’s airport Tuesday night after a second day of pro-democracy protests caused mass cancellations and disruptions at the busy travel hub.

Officers armed with pepper spray and batons attempted to enter the terminal, clashing with demonstrators who barricaded entrances with luggage carts.

The protesters left the building in the early hours of Wednesday, but vowed to return to the airport later in the day.

As the violent scenes unfolded, US President Donald Trump posted a tweet saying he had information from US intelligence that “the Chinese Government is moving troops to the Border with Hong Kong”.

“Everyone should be calm and safe!” he added.

Our Intelligence has informed us that the Chinese Government is moving troops to the Border with Hong Kong. Everyone should be calm and safe!

— Donald J. Trump (@realDonaldTrump) August 13, 2019

In the chaotic airport clashes, protesters allegedly beat at least two men they suspected of being undercover agents and zip-tied a mainland Chinese reporter to a luggage cart.

The reporter who was detained by protestors has been identified as an employee of state-run tabloid newspaperThe Global Times by the paper’s editor-in-chief.

Hong Kong TV channel iCable said the reporter was wearing a yellow high visibility vest and that protesters were demanding to see his press identification while shouting “gangster” at him.

It is understood protesters pinned him to the ground, seized his belongings and draped an “I love HK Police” T-shirt over him, as others tried to step in and stop the violence.

He was later taken away by an ambulance.

Fu Guohao, reporter of GT website is being seized by demonstrators at HK airport. I affirm this man being tied in this video is the reporter himself. He has no other task except for reporting. I sincerely ask the demonstrators to release him. I also ask for help of West reporters pic.twitter.com/sbFb0L3s92

— Hu Xijin 胡锡进 (@HuXijin_GT) August 13, 2019

Meanwhile China has denied a request for two US Navy ships to visit Hong Kong in the coming weeks, US officials say.

The officials, speaking on condition of anonymity, say the transport dock ship Green Bay had requested to visit later this month, while the guided-missile cruiser Lake Erie had requested to visit in September.

One of the officials said a specific reason was not given, but such a move was not unprecedented.

The move comes as Hong Kong chief executive Carrie Lam warned the city risked being “smashed to pieces”.

Protesters have severely crippled operations at Hong Kong’s international airport for a second day, forcing authorities to cancel all remaining flights out of the city after demonstrators took over terminals as part of a push for democratic reforms.

After a brief respite early on Tuesday during which flights were able to take off and land, the airport authority announced check-in services for departing flights were suspended as of 4.30pm local time.

Other departing flights that had completed the process would continue to operate.

The airport authority said it did not expect arriving flights to be affected, though dozens of arriving flights were already cancelled.

The authority advised the public not to come to the airport, one of the world’s busiest transport hubs.

On Monday more than 200 flights were cancelled and the airport was effectively shut down with no flights taking off or landing.

Passengers have been forced to seek accommodation in the city while airlines struggle to find other ways to get them to their destinations.

The airport protests and their disruption are an escalation of a summer of demonstrations aimed at what many Hong Kong residents see as an increasing erosion of the freedoms they were promised in 1997 when Communist Party-ruled mainland China took over what had been a British colony.

The airline protest is a blow to Hong Kong’s tourism industry. Photo: Getty

The central government in Beijing on Monday ominously characterised the current protest movement as something approaching “terrorism” that posed an “existential threat” to the local citizenry.

Meanwhile, paramilitary police were assembling across the border in the city of Shenzhen for exercises in what some saw as a threat to increase force brought against the mostly young protesters who have turned out in their thousands over the past 10 weeks.

Hong Kong leader Carrie Lam said the ongoing instability, chaos and violence have placed the city on a “path of no return”.

The demonstrators have shown no sign of letting up on their campaign to force Ms Lam’s administration to respond to their demands, including that she step down and entirely scrap legislation that could have seen criminal suspects sent to mainland China to face torture and unfair or politically charged trials.

Beijing’s usage of the term “terrorism” in relation to Hong Kong raises the prospect of greater violence and the possible suspension of legal rights for those detained.

Demonstrators have in recent days focused on their demand for an independent inquiry into what they call the police’s abuse of power and negligence.

That followed reports and circulating video footage of violent arrests and injuries sustained by protesters.

Some protesters have thrown bricks, eggs and flaming objects at police stations and police said they arrested another 149 demonstrators over the weekend, bringing the total to more than 700 since early June.

Police say several officers have suffered burns, bruises and eye damage inflicted by protesters.

The airport shutdown added to what authorities say is already a major blow to the financial hub’s crucial tourism industry.

Analysts said it could make foreign investors think twice about setting up shop in Hong Kong, which has long prided itself as being Asia’s leading business city with convenient air links across the region.

While China has yet to threaten sending in the army – as it did against pro-democracy protesters in Beijing in 1989 – the exercises in Shenzhen were a further demonstration of its ability to crush the demonstrations, even at the cost to Hong Kong’s reputation as a safe haven for business and international exchange.

-with Reuters