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.

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