Police from the Chinese mainland and the Hong Kong Special Administrative Region have dismantled a cross-border underground banking ring operating in Guangdong province and Hong Kong, arresting more than 170 suspects and freezing or seizing large amounts of assets, the Ministry of Public Security said on Tuesday.

The coordinated operation was carried out in May under the direction of the ministry, with public security authorities in Guangdong and other regions working alongside Hong Kong police.

Mainland police froze more than 15 million yuan ($2.23 million) in funds linked to the case, while Hong Kong police seized assets worth about HK$170 million ($21.7 million), according to the ministry.

The investigation began after Hong Kong police detected abnormal cross-border fund flows involving several Hong Kong bank accounts in September 2025 and requested assistance from mainland authorities.

The ministry's economic crime investigation bureau subsequently formed a special task force to investigate the case. Police found that the group had established shell companies on the mainland and in Hong Kong and exploited Guangdong's proximity to Hong Kong to build illegal channels for moving funds across the border.

The group allegedly transferred money through methods including "mirror settlement" inside and outside the mainland, fictitious trade, cash and gold smuggling, and virtual currency transactions. The network provided cross-border fund transfer services for criminal activities including gambling and fraud, involving large amounts of money, the ministry said.

During the operation in May, mainland police froze more than 15 million yuan and seized a large number of tools allegedly used in the crimes, including mobile phones and bank cards. Meanwhile, Hong Kong police arrested the alleged ringleader and two core members of the group and seized assets valued at about HK$170 million.

The ministry said the operation completely dismantled the cross-border underground banking network.

An official with the ministry's economic crime investigation bureau said mainland police and Hong Kong authorities have continued to strengthen cooperation in combating cross-border economic crimes.

The official said both sides will further deepen law enforcement cooperation and crack down on such crimes to safeguard financial security and the economic and financial order of the Guangdong-Hong Kong-Macao Greater Bay Area.