HK to Macau and then to Guangzhou for 3 days then to HK for a few days before returning to Australia

You had better to apply for a single entry Tourist L for visiting Guangzhou.

I want visa to china in hong kong

Usually, if you don’t have HK residence permit, it may be difficult to apply for mainland PRC visa from there. But you can have a try.
If you go to mainland PRC for sightseeing purpose, you need to prepare those documents including your passport and copy of its data page, the completed application form affixed with a recently-taken passport-style photo, your residence permit in HK, the round trip tickets and hotel reservation. And then submit your application to the office of the commissioner of the ministry of foreign affairs of PRC in HK to apply for the tourist L type.