China's police have conducted five operations to capture 846 suspects in a campaign the Ministry of Public Security launched in May to crack down on "money changing", a ministry official said.

Police in various regions have collaborated with the police of the Macao Special Administrative Region to crack a number of such cases, Chen Shiqu, deputy head of the ministry's criminal investigation department, said on Friday.

They have dismantled more than 100 "underground banks" and discovered more than 80 billion yuan ($11 billion) of capital flow involved in these cases, Chen said at a news conference held by the ministry in Beijing.

The police have also dismantled 263 organizations suspected of engaging in crimes deriving from "money changing", such as illegal business operation, illegal border-crossing, fraud and false imprisonment, Chen said.

"Money changers", or huanqiandang in Chinese, refers to those offering illicit cash exchange service in large amount for individuals or organizations, and lending money at exorbitant interest rates to gamblers, in Macao.

At a news conference held in July, Chen explained that casinos in Macao generally settle transactions in Hong Kong dollar.

"Money changers" circumvent China's financial policies, including the upper limit of cash that one is allowed to carry during exit and entry, and offer a large sum of cash in Hong Kong dollars to gamblers from the Chinese mainland, according to Chen.

Chen said on Friday the ministry has set up a headquarters in Zhuhai, a city in Guangdong province that neighbors Macao, and established a special working group to direct police forces in various regions to carry out the campaign.

The ministry has supervised the investigation of 16 major cases, Chen said, adding that border inspection authorities in Zhuhai, Shenzhen and Guangzhou have collaborated by identifying "money changers" and transferring them to the working group.

In October, a law to combat illegal gambling took effect in Macao.

According to the law, those operating unauthorized currency exchange services for the purpose of gambling shall be subject to up to five years in prison.

Chen said the move is a "firm step" the special administrative region has taken, and will be a "forceful legal weapon" to address the issue of "money changers".

The task to crack down on the illicit business, however, remains complicated, Chen said.

Pointing out that "money changing" is often conducted in a clandestine manner and directed by "financial supporters" through "remote control", Chen said it has engendered various kinds of crimes that undermine the security and stability in Macao, such as stealing, fraud, robbery, false imprisonment and blackmail.

Also, there is an ever more obvious trend where "money changing" serves as a way of money laundering for the illicit gains obtained from telecommunications and cyberspace fraud, Chen added.

"The ministry and the police of Macao have established a special collaboration system to tackle 'money changing'," Chen said. According to him, the special working group in Zhuhai has received 581 "money changers" sent back to the Chinese mainland by Macao's police.

Since this year, the Macao police have shared relevant information with police in the mainland on a regular basis, Chen said, adding that police on both sides are working closely to analyze the information they have.

Chen said the ministry will strengthen efforts to tackle relevant cases, and further consolidate cooperation with Macao's police.

For those who have engaged in "money changing", but whose offenses are minor and do not amount to the nature of criminal cases, the ministry will urge local police to persuade these people face-to-face and prevent them from relapsing, Chen said.

The ministry will also work with Macao's police to enhance public awareness of the special administrative region's law on combating illegal gambling, and advise tourists and workers there to follow foreign exchange rules and process foreign exchange through regular channels, he added.