SINGAPOREAN: OSAKA TO HONGKONG AND FURTHER TO SHENZHEN : VISA

I am holding a SINGAPORE PASSPORT and will be travelling to OSAKA for 3 nights stay and then travel to HK for another 3 night stay. Do I need a to apply for visa to enter HK FROM OSAKA? While in HK I will be going to SHENZHEN in the morning and back to HK in the night. Do I need to apply visa to SHENZHEN as well? Thank you.