Do I need a single or double entry visa?

I will be flying into Shanghai and then immediately out of Shanghai to Hong Kong, and then back to Shanghai a few days later. My flight getting into Shanghai and then the flight leaving for Hong Kong are not connected, so I would have to collect my bags and then check-in for the Hong Kong flight. In between these flights would I be going through immigration, and so technically entering China only to leave a few minutes later? Does this then mean I need a double-entry visa (as I return to Shanghai a few days later) or will a single entry suffice?