China on Tuesday introduced an “anti-online game addiction system” intended to protect players from the mental and physical perils of spending too much time in front of computers.

The system, which will encourage players to play less by cutting the benefits they gain in online games, is to be implemented by local internet companies that have signed a code of conduct drawn up by China's press and publications administration.

The move reflects fears about the social impact of popular “multiplayer online role-playing games” which have been blamed for encouraging sloth, truancy and even murder.

An estimated 25m Chinese play online role-playing games. These allow players to interact as characters ranging from warrior heroes to powerful magicians in vast virtual environments.

However, communist groups and newspapers have highlighted reports that many players are addicted to the games.

Under the new standard, up to three hours of play is considered “healthy” - and more than five to be “unhealthy”.

The anti-addiction system cuts in-game benefits to players after three hours. For most games this will mean awarding fewer “experience points” to fantasy characters and reducing the value of virtual goods such as magic weapons that they acquire.

After five hours online, players will be subjected every 15 minutes to the warning: “You have entered unhealthy game time, please go offline immediately to rest. If you do not your health will be damaged and the benefits you can win will be cut to zero.“

Leading games companies have agreed to the system to head off the threat of stricter regulation.

China's online games market is expected to grow 65 per cent to $633m this year, and will be the world's largest by 2006, according to CSFB, the investment bank. .

Such growth has won high valuations for Nasdaq-listed Chinese online games companies such as Shanda Interactive and Netease, which have promised to implement the system by late October.