No visa is required for ordinary passport holders from Singapore, Brunei and Japan to visit China for up to 15 days for business, sightseeing, visiting relatives and friends or transit.

If you are passing through Shanghai you can stay for 48 hours, provided you hold visas for onward countries, final destination tickets, have booked seats and you have a passport from Australia, Austria, Belgium, Canada, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, New Zealand, Norway, Poland, Portugal, Republic of Korea, Slovakia, Slovenia, Spain, Sweden, Switzerland, and the United States of America.

The type of visas issued varies from place to place.

A visa on arrival can be purchased for visiting Shenzhen at the border. The visa is available for most except people from USA. The cost starts at 150RMB.

This visa is only valid for 5 days and only for the Shenzhen area. It can be obtained from the border crossing with Hong Kong and Shenzhen airport.

From http://www.xbizy.com/article/69/2013-06-16/China-visa-information