Change your Working Permit and Residence Permit from employer A to employer B

You need to consult your new employer if they can obtain the necessary documents for you to apply for a Z visa. BTW, Z visa cannot be obtained within China, you need to go back to your homecountry to process the Z visa.
Foreign expert certificate is required for those foreign experts, scholars, teachers or managers to be working in Mainland of China and it is issued by the State Administration of Foreign Experts Affairs of the People's Republic of China. The requirements to apply for it include: foreign expert application form, your passport and its photocopy, your current visa and its photocopy, photocopy of Alien Employ-ment License of your new employer and its stamp, the contract between you and your new employer, the certificate for applying for foreign expert certificate by your employer, your physical exhimization certificate from local authorized hospital, your resume including education and working background, certificate of your highest degree, two recent 1X1 photos.