Police in China have raided more than 10 "underground banks," and arrested scores of suspects in a $23 billion sting operation that was nine months in the planning.

The Beijing Police said the banks had been used to illegally trade foreign currency and transfer money across international borders, and involved almost 140 billion yuan ($22.84 billion).

Like Us on Facebook

The sting operation involved more than 400 law enforcement officials, who seized some 800 bank cards, over 100 Internet banking digital certificates, and froze 264 bank accounts.

The police began the operation nine months ago when they first became suspicious of a man named Yao, who had been using various bank accounts to send money overseas. He only made transactions in yuan that were the equivalent of $50,000, which is the maximum that a Chinese citizen can legally acquire in foreign currency each year.  In one year, he transferred more than $5 million, police said.

Another suspect, known only as Yin, had registered a company in Hong Kong for trading metals. The company generated U.S. dollars, which Yin used to facilitate money transfers, according to Beijing police.

The "underground banks" were hidden in Beijing's Chaoyang, Dongcheng and Xicheng districts. During the raid trading procedures, capital flow, business networks and other questionable activities were uncovered.

The police said that rather than trading in cash, the suspects transferred money online or by cellphone, and they often did this out of their own homes while they borrowed, rented or bought others' bank accounts.

The underground banks have no financial supervision, and according to the Beijing police, they threaten the economy and financial security, and also encourage smuggling, money laundering and state assets embezzlement.

TagsChina Raids Underground Banks in $23 Billion Sting Operation, Underground banks, $23 billion, 800 bank cards, Yao, Bust, China Busts