China Transit Visa (G Visa) is issued to an alien who transits through China. Visas are not required in the following circumstances:

Visa-free entry for visitors: 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. For Mongolian citizens, it is 30 days visa free.

Visa-free transit

Visas are not required of aliens who hold air tickets to the final destination (third country or region) and have booked seats on international airliners flying directly through China, and will stay in a transit city for less than 24 hours without leaving the airport.

72-hour transit Visas exemption (carried out from Jan 1, 2013 on)

Visas are not required of passport holders of the following countries, who transit through Beijing Capital Airport, Shanghai Pudong Airport or Shanghai Hongqiao Airport, provided they hold valid passports, visas for the onward third countries, final destination tickets and have booked seats, and stay in Beijing or Shanghai for less than 72 hours.

The 45 countries include: Argentina, Austria, Australia, Belgium, Brazil, Brunei, Britain, Bulgaria, Canada, Chile, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Japan, Latvia, Lithuania, Luxembourg, Malta, Mexico, Netherlands, New Zealand, Poland, Portugal, Qatar, Romania, Russia, Singapore, Slovak, Slovenia, South Korea, Spain, Sweden, Switzerland, United Arab Emirates, Ukraine, The United States.

Restrictions of the 72-hour Visa-free Transit:
This regulation does not apply to passengers who travel on a return flight (e.g., USA - Beijing - USA), which means the destination and place of departure can not be in the same country.
The 72-hour visa-free stay only applies to transit via Capital International Airport. Passengers by train or any other vehicles should still apply for a visa in advance.
Visitors are not allowed to leave Beijing to other cities during the 72-hour visa-free period. They can only depart Beijing from Capital International Airport.
If visitors are unable to depart on time due to unavoidable reasons, such as flight cancellation or treatment of sudden disease, they need to apply for a visa from Municipal Public Security Bureau (PSB).

SHENYANG - Shenyang and Dalian, capital and port city of northeast China's Liaoning Province, respectively, launched 72-hour visa-free stays for foreigners starting on January 1, 2014.

Till now, Beijing, Shanghai, Guangzhou, Chengdu, Chongqing, Shenyang and Dalian have 72-hour visa-free services in place.