China's military has released a slick propaganda video showing a drill of armed troops quelling a protest in Hong Kong, in a thinly veiled warning to the city's pro-democracy movement.

The video, posted on social media on Wednesday by the People's Liberation Army (PLA) garrison in Hong Kong, has a caption in which the military declares it has the "confidence" and "capabilities" to maintain security in the semi-autonomous southern Chinese city.

The three-minute video showcases the PLA's tanks, helicopters, rocket launchers and other military hardware in action in Hong Kong, as well as heavily armed troops performing an anti-terrorism drill.

Meanwhile, hundreds of financial workers braved pouring rain to gather in central Hong Kong yesterday to march in support of the mass protests.