Police say they are keeping close watch on rampant illegal banking, which has been linked to the flow of billions of dollars in "hot money" every year.
Hot money is stolen cash that can be traced back to a crime, such as marked currency or new bills with consecutive serial numbers.
"We've spared no efforts in dealing with the illegal private banks; however, it is by no means easy to track them down," an official with the provincial public security department's economic crime investigation bureau told China Daily.
"Our bureau has been watching the rapid inflow of international hot money very closely, while tracking down the illegal banks," the official said.
The flow of international hot money grew in China in April and has been gaining speed ever since, said Li Youhuan, a researcher with the provincial academy of social sciences, citing the outcome of a recent study.
Official estimates of the hot money transactions stood at $87.9 billion in the second quarter of this year.
"The exact figure must be much, much higher than that," he said.
According to Li, much of the hot money has flowed in via the illegal private banks in Shenzhen, while Hong Kong has been an important entrance for the international hot money.
The recent decision of two banks in Shenzhen to impose quotas on ATM cash withdrawals has much to do with the abnormal inflow of hot money and the rampancy of illegal private banks.