The police said on Thursday that Ho Van Linh, 33, a native of the central city, was the mastermind behind the ring.

Following raids in six different locations in Da Nang on Monday, the police seized VND400 million ($17,100) and $4,800 in cash, a grenade, a rubber bullet gun, three iron swords, and financial documents related to the online gambling activities.

The betting pool of money came up to tens of thousands of dollars a day. Apart from taking the bets himself, Linh also assigned the job to others, who also took turns to collect money from the gamblers.

Four other members of the syndicate were also taken into custody.

It is unclear when the ring started. The case is being investigated further.

Vietnamese are known for their love of gambling. It is estimated that they spend at least $800 million a year gambling overseas, mainly in Macau, Singapore and Hong Kong.

Official figures show that Vietnamese spent $13 billion on the lottery between 2011 and 2015, Nikkei reported.

While the government has legalized sports betting, and allowed people aged over 21 with a monthly income of at least VND10 million ($445) to gamble at designated casinos on a pilot basis, online betting remains proscribed.