How do I get a 72 hour transit visa for Guangzhou airport?

I am flying Sydney, Guangzhou, Amsterdam. I have a 20 hour stopover in Guangzhou. How do I obtain the 72 hour transit permit at this airport? I hold both UK and Australian passports. I have not been able to get any help from my airline - they have advised me this permit does not exist. Can anyone advise me on this please.