Do I need a visa for 28 hours lay over in Shanghai.

I arrive into Shanghai on a flight from london on british airways which goes via Hong Kong where there is a change of planes taking two hours. 2 hours. I want to have 28 hours in the city of Shanghai and spend one night there before leaving on a flight to Melbourne with qantus. again this flight goes via Hong Kong but only to change planes. Can I get a 72 hour visa on arrival in Shanghai airport or do I need to get a visa before i travel.

thank you for your help