Melbourne - Hong Kong - Shanghai & Shanghai - Melbourne

Hi,
Assuming I'm in Shanghai for no longer than 144 hours, can I fly Melbourne to Hong Kong, wait in airport 2 hours for connecting flight to Shanghai? Or do I have to actually pass through passport control and stay in Hong Kong for a day before I can fly onto Shanghai?

I assume regardless which of the above is correct, I can then fly direct Shanghai to Melbourne (within 6 days of arriving in Shanghai).