You shall immediately go to the local entry & exit administration authority of the local public security bureau to apply for a passport loss certificate, and contact the embassy or consulate of your country in China with the passport loss certificate. After you apply for a new passport or temporary travel document, you shall apply to the entry & exit administration authorities of the local public security bureaus at or above county level for a visa renewal or reissuance.

Note: The above information is from “Welcome to China” and  only for reference.