Based on data from https://chp-dashboard.geodata.gov.hk/covid-19/en.html:
I'm surprised how many "imported" cases are still discovered daily, and that it's still a (fast) growing number. On the other hand, it's clear there are also plenty local cases.
at the airport not quite, suspects can be tested, and then held in Asia World expo until they get the all-clear result, it takes about a day to get the result, then there are free to get bus home.
The problem of asymptomatic patients remains, only testing everyone will discover those cases, I guess it is money, Government's will not fund the testing.