Satellite imagery appears to show Chinese armoured personnel carriers massed in a sports complex near the Hong Kong border in a sign Beijing may be ready to intervene against the ongoing pro-democracy protests.

The photos show what appear to be hundreds of the military-style vehicles in the city of Shenzhen, which is just a few kilometres from Hong Kong.

The pictures, collected by Maxar’s WorldView, show 500 or more vehicles  parked on and around the soccer stadium at the Shenzhen Bay Sports Centre just across the harbour from the Asian financial hub.

A CNN team in Shenzhen on Thursday morning reported witnessing  large numbers of uniformed members of the People’s Armed Police Force carrying riot shields and batons.

One officer was quoted by CNN as saying the troops had arrived for a “temporary assignment”, staying at the sports stadium. The officer did not confirm why the troops were stationed there.

Chinese state media have said only that the exercises had been planned beforehand and were not directly related to the unrest in Hong Kong, although they came shortly after the central government in Beijing said the protests were beginning to show the “sprouts of terrorism”.

The US State Department spokesperson said America was  “deeply concerned” about the Chinese paramilitary movement.

Another US official said Beijing had stationed large numbers of paramilitary People’s Armed Police “near and further out from Hong Kong”, in response to weeks of street protests in the territory.

The official said there was no sign they were moving towards the border.

The number of personnel was “in the thousands”, said the official, who did not want to be identified.

“They have amped up training and made it all pretty visible,” he said.

“There are no recent indicators that they are preparing to deploy.”

President Donald Trump tweeted Wednesday that US intelligence believes that the Chinese government is moving troops to its border with Hong Kong and that, “Everyone should be calm and safe!”

Beijing has been apparently reluctant to send in police or army units from the mainland or to mobilise the People’s Liberation Army garrison in Hong Kong to quell the unrest.

It’s seen as mindful of the devastating effect that would have both on the territory’s reputation as a safe and stable place to invest in, and as indication of the Communist Party’s failure to win over the hearts and minds of the city’s 7.3 million residents, 22 years after the former British colony was handed over to China.

Visual evidence from #space: The Maxar News Bureau released this #satellite image taken yesterday by WorldView-1 showing military equipment inside the Shenzhen Bay Sports Center outside of #HongKong. Reports say it’s Chinese troops: https://t.co/gRHprxzYSJ pic.twitter.com/NdAVSe5IoK

— Maxar Technologies (@Maxar) August 13, 2019

It would also be a shocking reminder of the PLA’s bloody crackdown on pro-democracy demonstrations centred on Beijing’s Tiananmen Square 30 years ago, which remains a taboo subject in China but is memorialised with a massive rally and march each year in Hong Kong.

Yet, mainland China is believed to have already dispatched officers to fortify the ranks of the Hong Kong police, and may also have planted decoys among the protesters in order to encourage more violent acts that could eventually turn ordinary Hong Kongers against the protest movement.

Such a change in sentiments does not yet appear to have happened despite rising violence surrounding protests and the shutdown of the city’s usually bustling international airport for two days after it was occupied by demonstrators.

-with AAP