The parents of a 13 year-old boy who fell to his death are suing Blizzard Entertainment, the makers of online role-playing game World of Warcraft, claiming that their son died re-enacting a stunt from the game.

Zhang Xiaoyi killed himself in December 2004 by jumping off a 24-story building in the northern China city of Tianjin.

Now 63 other families are to join the legal case, according to the official Chinese news agency.

Computer game addiction, or 'e-heroin' as it has been dubbed, is an increasing problem in China. According to the report one student cut his little finger to show his determination to kick his web addiction.

Zhang Chunliang, a Chinese cyber-addiction expert, maintains that there is no difference between being addicted to drugs and being addicted to internet games.

"A child's addiction to internet games means the ruin of a whole family," he told the news agency. "Indulging in a virtual cyber-world causes players to mix the virtual world with the real world."

China's online game market has generated $580m so far this year, and is the fastest-growing market in the world, according to research firm DFC Intelligence. The market is set to nearly triple in size to an estimated $1.7bn by 2010.