Going to work in China straight from Korea

Hi,

I have been offered a job to teach at a university in Chengdu beginning in late August/early September. I was wondering if it was possible to apply for my z working visa from here in Korea, and if so what I should tell the HR at the school to write on my letter of invitation and other documents before sending them? And if this is NOT possible, is the next easiest/closest way to get it by doing a stopover and application in Hong Kong on my way to the mainland? Thanks.