A Chinese visa is required for visitors from most of countries (for Singapore, Brunei and Japan, see info at the end). The guidelines for Chinese visa application have been changed recently. An invitation is normally needed for visa application (please check with your local Chinese consulate).
There are a lot of companies one can find online (preferably with local courier service) that can apply visa for you for a small extra service fee.
A citizen of Singapore, Brunei or Japan with an ordinary passport is exempted from a visa if he/she visits China's mainland for tourism purpose, business, or meeting and stays for no more than 15 days.