i want to know how could i do for process of visa

hi dear ,,, i am working in china in changchun ,,, my contract with my company is going to finish at the end of this month,,, but i am getting another job from another company in the same city in changchun ,, so i want to know how could i do for process of visa,,, i can join the next company by staying in changchun or i must have to leave china for once with new invitation letter,, and another thing if i would have to leave then i must have to go back to uzbekistan or i can get it from hongkong also?