Ministry spokesman Wu Qian suggested such a deployment may occur if the Hong Kong government requests it, multiple news outlets reported.
For over two months, political tensions in Hong Kong have escalated over a proposed extradition bill that would allow those arrested in the territory to be sent to mainland China for trial. Hong Kong citizens are concerned that their civil rights are slowly eroding under Beijing's control.
Asked how China's Defense Ministry would handle a rise of calls for Hong Kong "independence," Wu pointed to "clear provisions" in Hong Kong's Garrison Law, section 3, article 14, the Financial Times reported, citing the spokesman's comments at a news briefing.
Wu said the "behavior of some radical demonstrators ... is absolutely intolerable" and did not elaborate beyond pointing to the legal passage, the Associated Press reported.
The article stipulates that the Hong Kong government may ask for assistance from Chinese military troops stationed in the city "in the maintenance of public order."
Last Sunday, protesters surrounded China's main representative office in Hong Kong and defaced walls and signs. They also clashed with police.
Later the same day, men in white t-shirts — some armed with clubs — flooded the rural Yuen Long station, and stormed a train, attacking passengers with pipes, poles and other objects, according to video footage.
China has so far not directly intervened in the crisis but its state media denounced the vandalism at Beijing's Central Government Liaison Office in Hong Kong.
Wu on Wednesday echoed that sentiment, saying that "the behavior of some radical protesters challenges the central government's authority, touching on the bottom line principle of 'one country, two systems,'" according to The New York Times.
"That absolutely cannot be tolerated," he reportedly added.
Former British colony Hong Kong returned to Chinese rule on July 1, 1997 under a "one country, two systems" framework. The territory was guaranteed a high degree of control over its own affairs for at least 50 years.
— The Associated Press contributed to this report.