Layover of 12 hours at Guangzhou Airport, will i be allowed for short tour of the city

Oh, of course you can enjoy the short tour in town. You need to fill in the "embarkation/disembarkation card" on airplane before landing. After getting to the airport, go to the immigration to show the card, passport and the boarding pass, you will be given a stay permit, with which you will be allowed to leave the airport.