A 72-hour Visa-free Transit exist in fifteen cities in China, including Shanghai. It is allowed for passengers of 51 countries including Australia.
If you want to go out of the airport, you need to present your confirmed seat ticket departing from Shanghai less than 72 hours after your arrival at the airport and if your destination is not your native country a valid visa to enter that third country.
Leaving the city will be considered illegal since you do not have a visa for China but a free-transit visa for Shanghai.
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