Vietnamese police have arrested 13 people in Hanoi who allegedly helped gamblers bet $69m through b8ag.com.
The operation was run through a website which was hosted on an overseas server. It is believed Hoang Lai Nam, 41, was in charge.
The activity was largely found in Hanoi, alongside Hai Phong City, Thai Binh Province and Ho Chi Minh City.
As well as the arrests, Vietnamese authorities seized eight cars, multiple computers and mobile phones, worth around $240,000.
In 2017, Vietnamese authorities legalised sports betting for citizens aged over 21 and allowed people with a monthly income of at least ₫10m ($445) to play in a casino in the southern Phu Quoc Island.
Online gambling in Vietnam however, remains legal. Police are continuing to investigate the situation.