I'm living in Darwin, Northern Territory, Australia.

You should first prepare the relevant documents: copy of passport, a recently-taken Passport-style photo, proof of financial standing, the completed application form, permanent residence permit in Australia, flight itinerary, hotel reservation and travel plan. Next, submit two separate applications to China consulate general to apply for HK and Macau visas. You cannot post the applications. You need to submit in person or entrust someone else to do that on your behalf.