US senators voice support for Hong Kong protesters as military vehicles arrive in neighbouring Shenzhen

President Trump calls for calm, saying intelligence briefing showed a build-up of paramilitary forces

A tourist gives her luggage to security guards as she tries to enter the departures gate during another demonstration by pro-democracy protesters at Hong Kong's international airport on August 13, 2019. AFP

A member of the airport staff tries to stop anti-government protesters during a demonstration at Hong Kong Airport. Reuters

Passengers talk with a member of the airport staff after the announcement that all airport operations are suspended due to an anti-government demonstration at Hong Kong Airport. Reuters

Anti-government protesters react after the announcement that all airport operations are suspended due to a demonstration at Hong Kong Airport on August 13, 2019. Reuters

Hong Kong pro-democracy protesters (bottom) block access to the departure gates during another demonstration at Hong Kong's international airport on August 13, 2019. AFP

Two travellers react after protesters tried to block them from entering the departures gates area during another demonstration at Hong Kong's international airport on August 13, 2019. AFP

Protesters march against police violence in Hong Kong Chek Lap Kok International Airport, Hong Kong. EPA

Hong Kong pro-democracy protesters (C) crowd the area in front of the departure gates to block access during another demonstration at Hong Kong's international airport on August 13, 2019. AFP

US politicians from both parties have expressed support for protesters in Hong Kong as footage showed convoys of Chinese military vehicles arriving in Shenzhen, near the border of the semi-autonomous territory.

The vehicles were pictured on Tuesday 28 kilometres away from Hong Kong, where protesters have shut the airport for a second day.

Footage on social networks showed large numbers of camouflaged trucks and armoured personnel carriers assembling in the city.

The vehicles belong to the Chinese People’s Armed Police, a paramilitary force with close links to the People’s Liberation Army, local news networks said.

In one clip on Twitter, a column of military vehicles enter the Shenzen Bay Sports Centre.

US President Donald Trump urged caution on Tuesday, saying US intelligence informed him of the military build-up.

“Everyone should be calm and safe,” Mr Trump tweeted.

The Trump administration on Monday said the dispute was an issue strictly "between Hong Kong and China".

“The Hong Kong thing is a very tough situation," Mr Trump said. "I hope it works out peacefully.

"I hope nobody gets hurt. I hope nobody gets killed. I hope it works out for everybody, including China.”

Paramilitary forces are believed to have been gathering in Shenzhen since Saturday.

Chinese state media has described the build-up as preparation for “large-scale exercises".

Chinese riot police earlier conducted a drill with thousands of participants, in what was considered to be a warning from Beijing about its ability to end two months of protests in the global financial centre.

The UN has voiced its concern at the “escalation of violence".

Rupert Colville, spokesman for the UN High Commissioner for Human Rights, urged the authorities to act with restraint and “to ensure that the right of those who are expressing their views peacefully are respected and protected".

Chris Patten, the last British governor of Hong Kong before it was handed back to the Chinese in 1997, told BBC Radio that Chinese military intervention in the city would be a catastrophe.

In the US, Republican Senate majority leader Mitch McConnell and Democrat Speaker of the House Nancy Pelosi backed the protesters.

"The people of Hong Kong deserve the true autonomy that was promised, with the full rights guaranteed by the Hong Kong Basic Law and international agreements,” Ms Pelosi said.

Mr McConnell said that any crackdown by China would not be acceptable:

Senator Elizabeth Warren, who is running for presidential candidate in the Democratic primaries, also issued a statement announcing solidarity with the protesters:

The recent statements from Democrats and Republicans show the continued importance of the issue in the US.

Last June, more than a dozen senators from both parties issued a statement supporting the protests.