I hold Aust. passport and plan to visit HK and China. Could I apply the China visa in HK(where)

You can apply for China visa in Hong Kong, The Commissioner's Office of Foreign Affairs Ministry of P.R.China in Hong Kong:
Address
7th Floor, Lower Block, China Resources Building,
No.26, Harbor Road, Wanchai, Hong Kong SAR

Office Hours
Monday to Friday (except Hong Kong public holidays,)
9:00-12:00 14:00-17:00

1, Tel- Enquiry
24 hour Recorded Visa Information Service: 852-34132300
Live Answering Telephone: 852-34132424 (available at 10:00-11:00am, 3:00-4:00pm on workdays)

2, Fax: 852-34132312