australians applying for chinese F visa in hongkong

You may just go to the Embassy to submit the application directly during the office hours 09-12:00 & 14:00-17:00 from Monday to Friday except public holidays. You may also entrust a travel agency to apply for the visa for you. Since you are applying for a China visa in a third region other thna your home country, you may be required to provide additional documents. The address of the visa office of PRC in HK SAR is 7th Floor, Lower Block, China Resources Building, No.26, Harbor Road, Wanchai.
I advise you contact the office directly to enquire about the exact details by 24 hour Automatic Answering Telephone: 852-34132300 or Live Answering Telephone: 852-34132424 (available at 10:00-11:00, 15:00-16:00 on workdays).