[NotPaidToPost]

How would you proceed to "annex" your own territory?

HK is not Crimea (mentioned by someone else), it is Chinese but enjoys a high degree of autonomy until 2047.

[chatmasta]

You send a bunch of soldiers into the territory and say the treaty is canceled, 28 years early.

[DiogenesKynikos]

The PLA is already stationed in Hong Kong. They moved in during the early morning of 1 July 1997:

https://www.youtube.com/watch?v=koH6lGlcbn8