In priciple, you have to apply for your China work visa in your home country. But you may have a try in
Thailand.
The required documents are:
a The original passport with a validity more than six months and enough blank visa pages;
b One copy of completed visa application form in Chinese or English (two copies for US citizens), attached with one of the applicant's recent colorful front pictures of upper body (30mm X 40mm)
c. A visa notice or cable from an authorized Chinese organization and "Employment Permit for Foreigners in the People's Republic of China" issued by the Labor Ministry.