Australians entering China from Vietnam

Hello,

I am going to Vietnam for 4 weeks (28 Sept to 26th October), and would like to travel to China for 1 week (11 October to 18 October), on return flights from Ho Chi Minh City to Shanghai, and back to Ho Chi Minh city. Is it okay that I apply for a tourist visa for China from Australia ?

Do I still have time to apply by post (I need my passport back in time for travelling to Vietnam on 28th Sept) ? I live in South Australia so it's not possible to apply in person.

Thanks for your help.

Jasmine W