30 days extension without cancelling my m visa

Very very urgent and important question please.i came into china with m business type for one year but 30 days on each stay but i need to stay more 30 days now because my goods which I want inspect have not been finish. my question is can they give me 30 days extension without cancelling that one year m type they gave me in my country? my m type is most important to me. i cannot destroy it for the 30 days extension.