The circular says on-line game companies must develop a system that restricts a minor's playing time by canceling half their earned credits if they remain on-line for more than three hours a day. If the child plays for more than five hours a day all of their gaming credits will be taken away.

Most on-line games encourage players to play longer by rewarding them with more credits and virtue goods. "The system will only target minors who lack the self-discipline to control their playing time," said Kou Xiaowei, an official with the State Press and Publication Administration (SPPA).

"There has been controversy over what is the upper limit of 'healthy' playing time," Kou said. "We set three hours as the final limit based on a survey that found 64 percent of Internet users in China use it for less than three hours a day."

On-line gamers will also be required to register using their real names and identity card numbers which will indicate if they are under the age of 18.

The companies will have until June 15 to develop an anti-addiction system which must be fully tested by July 15 and implemented thereafter, according to the circular.

The circular was co-issued by eight government departments, including the SPPA, the Ministry of Education and the Ministry of Public Security.

In early March, China banned new internet bars from opening in 2007 as part of the government's campaign to combat the rising problem of Internet addiction. Some internet bars in China resemble huge discos with hundreds of computer stations surrounded by a high-tech decor where users play throughout the night.

Over the past few years, China has seen an alarming rise in the number of teenagers addicted to internet gaming.

A report released by the China National Children's Center claimed that 13 percent of Chinese internet users under the age of 18 were addicted to internet gaming.

Official statistics show that the number of internet users in China reached 123 million in mid-2006. About 15 percent - or 18 million - are under the age of 18.