Though a Z visa can be issued by the PSB of provincial capitals,said Z does not state employment shall be had only in one town or one city.I'm puzzled.
I thought a Z visa is the visa you need if you enter China to work.It is superceded by the Residence Permit,which specifies your school/employer,and where you are staying,ie your address.
Some provinces in China have PSB's based in their capitals who chose to issue backdated Z visas to louwai that have entered China on L's,and have subsequently found employment.I've had that done before.Contrary to what has been written about this,it's NOT ILLEGAL!
But if you've got an L issued from within China by a local PSB office,that kind of L visa is not able to be 'converted' to a Z inside China.
If you've that kind of L visa you can do a visa run to HK or Ulaanbator(cheaper) or any other neighbouring foreign country to get a Z,and then re-enter.According to a good recruiter I know well,having to return to your homeland to effect said change is no longer necessary for louwai with L's in China who have got letters of invitation from employers.It seems some restrictions that were introduced duoring 'one dream year' have since been lifted.