If you are coming to China for travel,you should obtain a touristvisa from the Chinese Embassy or Consulate in your home country. It is more convenient for tourists booked through Chinese travel agencies to get group visas for their visit to China. Tourist visas are usually good for two months, but can be extended for an extra month at the Foreigners Section of the public Security Bureau. If you want to continue traveling in China for more than three months, you will have to leave the country,get a new visa,and cone back. It is not too much trouble to go to Hong Kong and apply for a new visa. You can get a new one is two or three days.(Even though Hong Kong is now officially part of China, going there still counts as leaving the country.) for a little more money you can get a six-month visa from the China Travel Sdervice in Hong Kong. More adventurous souls can go to Mongolia, but you have to get another visa to go there. Whatever you do, don't stay in the country longer than your visa allows. The fine for overstaying your welcome is 500 yuan (US$55) perday!
It is wise to carr your passport with you at all times, as you need it to register in hotels, buy plane tickets and change money. Also, sometimes there are random checkpoints at night for passengers riding in taxis, of you can't produce identity proving who you are, you could be fined a whopping 5 yuan. However they usually don't bother with foreigners. if you lose your passport, you should report immediately to your embassy, as well as tell the public Security Bureau.