How to process Working Visa for foreigners?

I just completed my bachelors degree from Xi'an China in Mechanical Engineering. I applied in some companies in China. One of the company offered me Job and they are ready to give me working visa. but they don't know how to process visa for foreigners.

I am Pakistani national but i was born and lived in Riyadh Saudia Arabia. Now a days i am in Xi'an China on student visa. My visa is expiring in july i would like to change and transfer to that company.

Kindly guide me please.
i should process my visa from Riyadh or from here in China?

Thanks