My sister's daughter had a very bad diaper rash before. Her pediatrician recommended her to use 'Zincofax' and the diaper rash disappeared in a short period of time. We bought in Canada, not sure if you can get it in Hong Kong. However, I still have 3 new bottles, let me know if you are interested.
Here is the information about Zincofax:
http://www.rxmed.com/b.main/b2.pharmaceutical/b2.1.monographs/CPS-%20Monographs/CPS-%20(General%20Monographs-%20Z)/ZINCOFAX.html