Hopefully no emergencies will occur during your visit to China but, just in case, here are some tips on how to deal with them.
In China, the Public Security Bureau (Police) is responsible for public safety and order. In addition to traditional police responsibilities, the Bureau is in charge of issuing visa extensions.

If you lose something of value, please notify immediately your hotel, tour group leader, transportation authorities and/or the police. If your credit cards or traveler's cheques have been lost or stolen, call the issuer as soon as possible. If you find yourself in a serious situation, you might also contact your embassy and/or consulate.

If you lose your passport, you should report the matter as soon as possible to the nearest Public Security Bureau (Police) and to your embassy or consulate in China. In order to get a new visa from the Chinese authorities, a Police report about the loss/theft will be needed.

For any other emergency, you should contact your hotel staff for assistance or dial: 110 for the police, 119 in case of fire or 120 for an ambulance.