Entry to HK from Mainland China

I hold an Indian passport. I will be flying into HK from India and from there, wish to travel to mainland PRC for about 12 days. Then my return flight to India is from HK. So I need to re-enter HK from mainland PRC (shenzhen area). Can I do that? Do I need to obtain a new entry permit to HK from mainland PRC? Ifyes, can I get it from mainland or need to apply in advance?
Please advise.
Thanks
Ani