Dear Pippen,
Congratulations, these are stunning photos (again!).
I think it could be a female Northern Sparrowhawk. The first picture could show well the proportion of tail to the body and the second one could show well the length of wings. Both wings and tail are long in proportion that is favour to the Northern Sparrowhawk, but not the Japanese Sparrowhawk (long wing, short tail) and the Besra (short wing, long tail). Moreover, the secondaries seem not budge (but it could depend on the angle of view).
Many fine bars on underparts indicating that is a female individual also show quite different to the Japanese Sparrowhawk and the Besra. Upperparts are rather uniform grey (except some darker on lesser coverts) also indicating that could be an adult. Eyebrow is also prominent, although it seem a bit thin comparing to other birds I have seen before.
I would also like to see any comments by other birdwatchers to this bird. If it is really a Northern Sparrowhawk, these are the first photos of this species in Hong Kong (as far as I know!).
Tung
