Hi Hoanglien,
I’m located in New York at the moment, I’m also in the process of getting the Z visa. There are 3 steps, and the process will take 1 – 2 months.
Step 1: Passport verification. This takes about 2.5 weeks. My passport will need to be authenticated by the local government first, and then it will be verified by the Chinese consulate. It’s much easier to pay for a China Visa agent to do all the leg work.
Step 2: Work permit. The employer will do this step and provide some paper work in order for me to get a temporary work visa in New York before I enter China.
Step 3: Residence permit. Apply in person. However, the applicant will need to do a health check first, and to provide the original of health certificate along with other required documents.
Are you also going through all these steps from Vietnam?
Good luck!