AU-CAN-HKG-CAN-AU - double entry Visa, right?

Hi
We are flying from AU to Guangzhou, and from there, taking the train to from GZ East railway station HKG to visit for first couple of days of trip, before returning by train from Hung Hom to GZ East again and attending Canton Fair, before returning to AU. Can you pls confirm that we need double-entry Visas for CN in this. Are?
Thnx/Rgds
J