One dealer in Kowloon City, Kwong Chi-hung, said there were times when his shop had been jammed solid with children, all looking for the latest cards during break-times. On some mornings, a crowd would be waiting for him when he arrived to open his shop.

Mr Kwong said some cards were more sought after than others. Cards based on current television favourites such as Dragon Ball were more valuable. Other cards with special features such as reflective or transparent backgrounds were limited editions and, therefore, the most desirable.

Mr Kwong said card collecting had maintained its popularity, and even attracted adults, because many people were involved in dealing and speculating. Some cards sell for $2,000. Cards made in limited editions in Japan become valuable by the time they reach Hong Kong.

With such prices, it was only a matter of time before organised crime became involved. Last week, police broke up a counterfeiting operation, confiscating fake cards worth $2.2 million.

Mr Kwong said he believed most collectors hoped to make money from dealing in the cards, with only two out of 10 people collecting purely from interest.

Meanwhile, social workers have noticed an unhealthy side-effect of the craze among young people.

Philip Choi Shing-kiu, president of the Hong Kong Social Workers' General Union, said: ''Teenagers are spending far too much money on this hobby. It's crazy. The prices have been pushed up to unreasonable levels. For many, it has stopped being just a hobby.'' He said in the temporary housing area where he works, he has encountered many children dealing in the cards. He has also come across cases where children have been so caught up in the craze, they have stolen from their parents to finance their habit.

And Mr Choi believes it is a big problem with wider implications because it influences children's values.

He said: ''It is teaching young children to speculate, to use money to make more money as quickly as possible.''