Is this possible and if so what visa's would I require?

Dear Sir, Madam

I am a single male British passport holder - I want to visit China alone. My plan is to fly from London to China Shenzhen where I have resident Chinese friends. I would like to stay there for a week or two and then go to Hong Kong for a visit and then come back to Shenzhen for a further period of a week or so and then fly back to the UK. Any further information would be greatly appreciated. I very much hope you are to help me with this enquiry.

Thank you

Yours faithfully

Mr James Hedgeland