You need the following documents:
1. Valid passport with at least 6 months validity and 2 blank pages.
2. 1 certificate-sized photo(3cm X 4cm).
3. A authentically fulfilled visa application form.
4. Valid residence visa in Japan and its copy.
5. Hotel booking in China and round-way air ticket.
If you are live far from Tokyo, you can apply for
the China visa from any of the Consulate of China in
Fukuoka, Nagasaki, Nagoya, Osaka or Sapporo.
You can apply for the visa through a travel agent. You can get the name list of the travel agencies from the China consulate where you will apply for the visa.

Hi Suzanne. JTB Travel offer a service where you send the documents to them and they get the visa and send it to you on your behalf. I found it expensive though at around Y30,000 but its another option if you find you just cant get into the embassy to do it yourself.