Short visit to Hong Kong with a 1 entry visa

Hello! I am Italian and I have a 1 entry tourist L type that I'll be using to enter the country in Beijing. I will then move to Shenzhen for a few days, before going back to Beijing for my return flight. Is there any way I can visit Hong Kong during my stay? If I go to Hong Kong and then fly back to Beijing (to get my international flight), am I eligible for the 72 hours free transit?
Thanks!