Getting my Z type extended in Guilin, China - will they take my passport?

Hello, I am an American living in China to teach English for about five months. The company that hired me wants to take my passport and get my Z type extended for me, but I'm afraid to let them take it and would like to go. In the US, when you apply for a visa you have to send your passport in...do you have to do that here or do I have to leave my passport with anyone? I'm terrified of leaving my passport in the hands of anyone. What do you think? Does anyone know anything about this?