change a company and apply for a new Z visa

hi ,, i am working for a company i have z- visa,, but company is not following the contract and i am in trouble now,, because they are not giving me salary and even no work... i want to cancel the contract with company because another company is offering me job here,, i want to know if the company in which i am working now will cancel my visa,, so then is it possible for me to get visit visa by staying in china and then go to hongkong and then change my visa into z-visa again using the invitation letter from the new company ,, or i must should have to go back first,, kindly reply