Crusing

I have clients who are on a cruise that docks in Beijing for 3 days, then it continues to Seoul, Korea then ends in Shanghai. One pair of clients are staying in in Shanghai for 4 nights, the other departing Shanghai when cruise ends to fly back to Australia. All are Aust and NZ passport holders. I have been advised as they are entering Beijing and exiting going to another country that then they can start another Visa Free period in Shanghai, is this the case. It is a grey area around cruising.