I fly in and out of HK a total of three times over a month period, do I need 3 visas?

I am flying from London to HK and staying for 4 days, I then fly to Shanghai for 2.5 days, then I fly to Tokyo for 2.5 days, then I fly back to HK and stay for 4 hours in the airport before then flying to Australia. I return to HK a week later to stay in the airport for 6 hours before flying back to London. I am an Australian Citizen but a UK resident.

Do I need to apply for three entry permits? and do I do this every time I re-enter HK?