It should be noted that the mainland govt. doesn't need to mobilize troops. The 6000-strong combat-ready PLA Hong Kong Garrison is already in Hong Kong. The only way for them to enter is if the Hong Kong govt. gives permission or the violence/demonstrations escalates to a point where troops need to be sent in or if the garrison is provoked. Otherwise, it will likely be ignored like the 2014 Umbrella Movement in Hong Kong and no military will be sent in.

https://en.wikipedia.org/wiki/People%27s_Liberation_Army_Hon...