A South African casino chain has uncovered an elaborate gaming racket which could have cost the industry millions of dollars.

The fraud involved the subtle marking of playing cards produced by South AfricaÀs only manufacturer, and enabled gamblers to know when high cards were coming up.

The ruse was uncovered by police when casino managers realised they were losing an unusually large amount of money. Investigations are now underway to establish whether casinos outside South Africa who buy cards from the same manufacturer have also been affected.