hi, I am a singapore student currently on exchange programme in shanghai china.

I am currently holding a F visa which grants me a single entry into china for 180days.

Is it possible for me to travel to hongkong over the weekend and back to shanghai again?
will it then be considered as multiple entry into china and I would have my visa void upon return to shanghai?

(I am not too use about hongkong being 'part of china' for visa.
Thanks