Chinese officials have busted the country's largest-ever underground banking ring, involving transactions totaling $64 billion.

Some 100 suspects from eight gangs have been detained since police in eastern China launched the investigation last September, according to official state media.

The gangs were thought to be linked to a ringleader who allegedly operated multiple shell companies in Hong Kong engaged in money laundering and foreign exchange transactions.

China has strict capital controls -- citizens can only move around $50,000 out of the country each year.

The restrictions have given rise to a shadowy world of money laundering -- via unique means from fine art buys to casinos in southern China -- that helps people send funds abroad. While some of that money comes from honest earnings, a portion is believed to have been obtained via corruption or fraud.

Related: China's anti-corruption crackdown reaches U.S.

Over the past year, officials have issued arrest warrants for 56 people, frozen 3,000 bank accounts, shut down 37 unlicensed financial institutions allegedly laundering money and reviewed over 1.3 million suspicious transactions, reported state media.

Police busted another 10 unapproved banks this week, allegedly linked to about 51.6 billion yuan ($8.1 billion) in illegal transactions.