Chen Daoxiang, the commander of the People's Liberation Army's (PLA) Hong Kong garrison, said that violent clashes would not be tolerated and that the Army was determined to protect China's sovereignty, the South China Morning Post reported.
Hong Kong, a former British colony nowadays retains significant autonomy from mainland China and was handed over to Beijing in 1997.
The video, posted to social media, begins with a soldier shouting: "All consequences are at your own risk."
Tensions are high in Hong Kong after weeks of anti-government protests that began in early June in opposition to a now-shelved bill that would have allowed extradition to mainland China.
But these protests have evolved into a catch-all movement against the local government and are causing disruptions. The protesters are now demanding an independent inquiry into police violence, resignation of the territory's Chief Executive Carrie Lam and democratic reform.
Chen Daoxiang's made the warning at a reception in Hong Kong celebrating the 92nd anniversary of the Chinese military on Wednesday, when the garrison released the promotional video that stated that troops stationed in the city were able to protect its long-term stability.
In his first comments on Hong Kong since the protests erupted, he said that the demonstrations had "seriously threatened the life and safety of Hong Kong citizens, and violated the bottom line of 'one country, two systems'.
"This should not be tolerated and we express our strong condemnation," Chen was quoted as saying by the daily.
The Army video, posted to the Chinese social media site Weibo, showed lines of troops carrying shields and batons performing anti-riot drills.
It showcased tanks, rocket launchers, water cannon and barbed wire before featuring heavily-armed troops descending from helicopters and shooting their way through the streets and into people's homes.
Troops can be seen marching with a red warning flag telling rioters to "stop charging, or we use force".
Protesters can also be seen being arrested and walked, with their arms tied behind their backs, to "detention points".
Chen said the garrison resolutely supported Hong Kong's Chief Executive and the city's police in maintaining law and order.
Observers say the video was likely to have been filmed in Hong Kong because the local Cantonese dialect was spoken in the video and it featured a Hong Kong taxi and a flag almost identical to one used by the territory's police.
( With inputs from IANS )