z visa china

Hi
There are job offers on- line to work in PRC, but they are vague about Z types which I understand you need to work in PRC. How would one go about getting this - these agents don't give full information on how to obtain one. I do not wish to go to PRC to establish I need a z type and then have problems etc

Can anyone advise is it easier whilst in uk or do I travel to PRC on a job offer to apply then (the last one I am not keen on)
thank you