Birth Certificate from China

My mother was born in Guangjou (Canton) in a village in 1931 but has lived in PNG and Australia since 1964. She has unfortunately allowed her Australian passport to expire and now needs to apply for a new passport. To do so she needs to obtain a birth certificate from PRC even though she never has had one. What is our best course of action in either obtaining a birth certificate or statement which says that she does not have one.