Do we need visa to Re-enter Shenzhen from HK

We plan to visit Hangzhou & Fuzhou from 30/10/2015 to 12/11/2015 (Total 14 Days) & will transit in HK on our return trip from 12/11/2015 to 15/11/2015.
Are we allowed to go into Shenzhen on 13/11/2015 without an entry permit?
As we understand, from Singapore, we can only stay for 14 days without entry permit in China.