Because the Registry is divided into 45 international classes in respect of goods and services, your trademark will only be protected in the class that you register it in. This is similar to many other countries in the world. Only if you are the owner of a well-known trademark, can the scope of protection for that mark be extended to other goods and services. Registering your trademark allows you, the owner, the exclusive right to use that mark and prevent others from using that mark or other marks that resemble your mark without authorization.
A Hong Kong trademark registration only lasts for 10 years, but can be renewed for 10 years after that.