Can I switch from Student X visa to Work Z within mainland China?

Hello- I am currently on a student type which expires on July 31, 2015. I have secured a job in Taiyuan, Shanxi and have all the necessary documents to apply for a work Z (letter of invitation etc). But I have been told I can only apply for that type from outside the mainland. Is it possible to apply for a work type within the mainland or must it be done from outside the mainland?