Travelling to China through Hong Kong

Hi,

I am a UK citizen travelling to China for two weeks. I have a single entry visa for my stay during these two weeks in Nanjing. I intend to visit a relative in Zhuhai between the two weeks in Nanjing. I have booked a return flight from Nanjing to Hong Kong, from there I will take the ferry over to Zhuhai. Entry to HK will be fine as I have a UK passport.

Will I have issues getting into Zhuhai and also when I return to Nanjing?