Firstly there isn't one case confirmed in HongKong yet.
Secondly, the virus could take up to 2 weeks to start showing symptoms and it is only until recently the method to detect this virus efficiently had been discovered.
This is a new virus, and its behavior takes time to understand.
[0], [1]
I agree this is a new virus we know little about, but did you know folks in Wuhan were still gathering in crowds without any precautions [2], and ppl got caught spreading so-called fake news of this virus?
[0] https://twitter.com/alvinllum/status/1219911842723553283
[1] https://news.rthk.hk/rthk/ch/component/k2/1504214-20200122.h...
[2] https://twitter.com/Xhnsoc__Redflag/status/12194676125282181...)