The ring, led by 28-year-old Nguyen Thi Huong Ly and 24-year-old Nguyen Duc Manh, utilized online gambling methods under the guise of games like poker and lottery, the ministry said. The ring had servers overseas and cooperated with several clients inside Vietnam.

The clients in Vietnam used phone numbers and social media for players to contact and transact with them. Players transferred cash into bank accounts provided by the clients, or paid through top-up cards.

Ly was in charge of creating clients’ accounts on the ring’s website for players to perform transactions. She traveled from Hanoi to Saigon last month to rent a location for her accomplices. She and Manh guided several people in using their personal bank accounts to perform transactions and play the games on offer.

The total amount of money transacted by the gambling ring since January last year amounted to around VND20 trillion, police said.

Ly, Manh and 18 others were arrested by police in Hanoi and Saigon on Wednesday.

Vietnam has relaxed its stance on gambling as a "social evil," legalizing sports betting in 2017 and allowing, on a pilot basis, people aged over 21 with a monthly income of at least VND10 million ($432) to play in a casino on the southern Phu Quoc Island.

But all other forms of gambling remain illegal.