what do i need to have for me work in china?

To enter and work in China, a China work visa is necessary. To apply for a China work visa, you have to ask your Chinese employer to provide you the "Invitation Letter of Duly Authorized Unit" or "Confirmation Letter of Invitation" and work permits for foreigners for your China work visa application.

My employer is an american firm that works only on dry docks in shanghai, What do i need from them in order to travell