This is the Lychee stink bug, the bane of many farmers, look for them as they infest trees like Longan and Lychee trees and suck the sap.
A great place to find these are in Tai Po Kau nature reserve. These are the colourful juveniles. The adults are almost uniform in appearance and quite drab by comparison.
Fascinating fact: The females always lay exactly 14 eggs!
Their name comes from their foul smelling, and long lasting excretion, to ward off predation.
Click on the images below for a higher resolution picture.
Here a page from my book on bugs detailing more about shield bugs in general.... order your copy today at https://www.wildcreatureshongkong.org/orderbooklet before the print run is out.....
Here a just hatched nymph...so cute.