Satellite images have revealed a massive build-up of military vehicles in a stadium near the border of mainland China and Hong Kong.
Protests have been ravaging Hong Kong over the last two months as demonstrators voice anger towards Beijing's influence in the financial hub. They have also clashed with police, including in a violent brawl at Hong Kong's airport on Tuesday night.
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The demonstrations have been sternly condemned by China, which said some of the protests were no different to terrorism and those involved should be punished.
Images captured on Monday and released by Maxar Technologies have now revealed China has built up an array of military and security vehicles at the Shenzhen Bay Sports Center, which is located near the Chinese border with Hong Kong.
The pictures appear to show roughly 100 armoured vehicles in the stadium, which is normally used for table tennis and football competitions.
Chinese media has insisted military exercises in Shenzhen, including a procession, were planned ahead of time and are not related to the Hong Kong demonstrations.
However, speculation that China could be planning to increase its presence in Hong Kong is concerning the United States. A spokesperson for the State Department said Beijing should continue to allow Hong Kong to exercise its freedoms.
"The United States is deeply concerned by reports of Chinese paramilitary movement along the Hong Kong border. The United States strongly urges Beijing to adhere to its commitments… to allow Hong Kong to exercise a high degree of autonomy."
On Wednesday, US President Donald Trump tweeted that US intelligence suggested the Chinese government was "moving troops to the border with Hong Kong".
"Everyone should be calm and safe".
Hong Kong is part of China under a 'one country, two systems' framework which allows Hong Kongers a level of autonomy. Protests were largely spurred on by a proposed Bill that would allow people on trial in Hong Kong to be extradited to mainland China.
Flights in and out of the city were disrupted earlier this week after the airport became the site of a massive sit-in. However, demonstrations at the airport have mostly ended after a court injunction was granted, limiting where protests could happen at the site and giving police greater powers to remove people.