(CNN) -- Police have smashed an illegal betting syndicate in Macau for allegedly taking the equivalent of US$645 million in bets on World Cup matches.
It's believed to be the biggest ever raid on an illicit football bookmaking racket in the Asian casino capital, according to police.
The gambling ring used three hotel rooms to take internet and phone bets from around the world, a first coordinator for the Macau Judiciary Police told CNN. One gambler placed a bet valued at around US$5 million, initial investigations found.
Police arrested some 22 people from mainland China, Hong Kong and Malaysia in the raid on Thursday. Two of the suspects, from China and Malaysia, were believed to be the ringleaders of the syndicate.
Officers seized cash worth around US$248,000, along with 17 computers, at least 10 cell phones, and betting slips.
A second gambling syndicate was busted in the same hotel hours later, with police arresting four Chinese men early Friday morning. According to police, the second betting ring took around US$645,000 in illegal bets on World Cup matches in a single day.
Police have not released the name of the hotel.
The arrests are part of a cross-border campaign to crack down on illegal betting in Macau, Hong Kong and China's southern Guangdong province around the World Cup. Authorities from the Pearl River Delta region are also cooperating with Interpol and seven other Asian nations to tackle illicit gambling.
More than half of the world's illegal sports bets are placed in Asia, according to a recent study by the International Center for Sport Security and Paris Sorbonne University.
Since the tournament began, Hong Kong police have arrested a total of 39 suspects over illegal gambling and seized betting slips worth around US$10 million, according to the South China Morning Post.
The city's legal gambling authority, the Hong Kong Jockey Club, is the second biggest betting operator worldwide. The club said illicit sports betting in Hong Kong generated an estimated HK$500 billion (US$64.5 billion) last year -- almost four times the amount the Jockey Club turned over in the same period.
In Singapore, 15 people have been arrested for allegedly receiving illegal football bets equivalent to US$640,000 in the past two weeks, police said Monday.
Police in Malaysia have also arrested dozens of suspected illegal bookmakers since the World Cup began.