Layover in Shenzhen and Guangzhou

Hi! I just booked a return ticket from Melbourne to Hanoi with a 22-hour layover (overnight) in Shenzhen and a 5-hour layover in Guangzhou on the return leg. I was just wondering if I need to apply for a transit G type and how much will it cost, (I've read $30 in one place and ~$100 in others), where do I apply (I've checked and the Consulate in Melbourne do not accept visa application and it has to go through commercial service). I hold a Vietnamese passport. Thank you!