Hong Kong (CNN)Chinese authorities say they have busted an underground money-smuggling ring used to launder more than $4.4 billion through the Asian gambling hub of Macau.
The case is a high-profile example of Beijing's crackdown on attempts to dodge its capital controls, which it has tightened in recent years to prevent money from flooding out of the country and destabilizing the economy.
Macau's Judicial Police said the syndicate was formed in 2016 and relied on point-of-sale machines -- the devices used by shops to conduct transactions with credit cards or debit cards -- which were smuggled in from China.
These in theory would allow Chinese citizens to make withdrawals from their bank accounts that appeared to be domestic transactions, thereby avoiding China's strict limits on how much money people can move across its borders.
Wealthy Chinese nationals living in the mainland have long sought to skirt the country's capital controls by moving money through Hong Kong and Macau. The cities are technically part of the People's Republic of China but governed as special administrative regions, with their own currencies and far fewer restrictions than mainland China on moving money internationally.
China's state-run Xinhua News Agency said authorities found evidence that the group, run by a suspect surnamed Xu, was using the point-of-sale machines to allow gamblers to secretly cash out their casino winnings in Hong Kong dollars and Macanese patacas.
Thirty-nine people were arrested in a series of coordinated raids across China and Macau earlier this month in connection with the case, Beijing police said on their official Weibo account. Macau police said they seized 32 mainland point-of-sale machines.
The case could bring increased scrutiny of Macau. Beijing has vowed to crack down on economic criminals and keep the yuan stable amid the ongoing trade war with the United States.
The Chinese government has spent vast sums in recent years to prop up its currency as its economy has slowed down. As a result, some investors have sought to move money into more attractive investments elsewhere.
Chinese nationals are not allowed to withdraw more than 100,000 yuan (about $15,000) a year overseas using domestic bank cards.
Macau poses a unique risk because it is the only place in China where casinos are allowed to operate legally, and the cash-intensive nature of the industry makes money particularly difficult to track.
But in a note to investors, analysts at Sanford Bernstein said the police action does not appear to be "materially different" from similar crackdowns and "this activity is part of an ongoing campaign against underground money transfers and illegal use of UnionPay (a Chinese financial service) which has been in force for several years."
Vitaly Umansky, a senior research analyst at Bernstein who covers the global gaming industry, said Macau authorities have increasingly been cracking down on illegal use of point-of-sale machines and have been making arrests every six to nine months.
Last summer, Macau's Monetary Authority ordered financial institutions to crack down on the illicit modification of point-of-sale machines, after a similar case was uncovered.
"What Macau has really gone after is all of these illegal POS (point-of-sale) devices," Umansky said.
Umansky said it's unclear how authorities came up with the $4.4 billion figure. That number was only mentioned by police in mainland China; Macau's Judicial Police said it seized $3 million from five accounts.
"They never really tell you what it means," Umansky said.