But the gang's leader, Tran Quang Truong, 30, has gone into hiding and the police are looking for him.

They said the organizers of the gambling ring had set up a system of tier 1 and 2 agencies through which their clients could buy virtual money to play online card games.

They could convert the virtual money back into cash whenever they wanted. The clients could make their transactions either directly at the agencies or through banks.

The total value of these transactions have been estimated at nearly VND4 trillion ($170 million), and the police have frozen more than VND6 billion ($256,000) in many bank accounts as part of their investigation.

Vietnam has relaxed its stance on gambling as a "social evil," legalizing sports betting in 2017 and allowing people aged over 21 with a monthly income of at least VND10 million ($445) to play in a casino in the southern Phu Quoc Island.

But online betting remains illegal.