More than 100 officers from the Ministry of Public Security and the Central Highlands province of Gia Lai raided 20 locations in the central city of Da Nang, including the house of alleged kingpin Huynh Ngoc Anh in Son Tra District, and Gia Lai.

The police had been keeping tabs on the gang for several months.

Investigators said Anh was running sports betting, an online casino and online lottery through Bong88.com, Bong88.net, Booking 88.net, and SmartBooking88.net with servers based overseas.

Players had to create accounts and buy virtual currency with real money to use in the gambling.

The network had been in operation for a long time and attracted thousands of gamblers and stakes of around VND3 trillion ($128.92 million) this year alone, investigators said.

Vietnam 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 ($432) to gamble in a casino on the southern Phu Quoc Island.

But online gambling remains illegal.

Illegal gambling and organizing it carry fines of VND10-50 million ($430- 2,150) and jail terms of three to seven years.