By Wei Gu 

China is trying to regain control of the cash flowing across its leaky borders and the effects will be felt around the world.

Beijing technically bans its citizens from buying overseas properties and stocks, and limits the money they can transfer abroad to $50,000 a year. Despite these rules, wealthy Chinese have found ways to move their money across the border, making them the biggest international buyers of properties in places like the U.S. and fueling a boom in Macau's casinos.

Underground channels--such as the money-exchange shops found across Hong Kong--have flourished in recent years. Some Chinese banks have quietly provided services to funnel customers' money across the border to boost their businesses.

"There seems to be a desire to tighten," said Oliver Barron, head of investment bank North Square Blue Oak's Beijing office. "The government is reacting to perceived outflows as Chinese businessmen want to get their money out."

The government has a lot of leaks to plug. These include longstanding strategies such as businesses over-invoicing their purchases or individuals using informal money-transfer networks. Other methods are more controversial, such as a Bank of China program that allowed clients to move large sums abroad. In the gambling center of Macau, the rich have used junkets, which lend them money in the former Portuguese territory and collect the debts back home. Less wealthy gamblers use their UnionPay cards, China's only domestic bank card, to make fake purchases, pocketing the cash.

China's gambling capital is among the first to feel the chill. Macau's casino revenue fell for a second straight month in July, dropping 3.6% from a year earlier.

Grant Bowie, chief executive officer of MGM China Holdings Ltd.-- MGM Resorts International's China venture--said at a news conference this week that China's moves to strengthen capital controls represent "a significant policy shift" that has made Chinese visitors to Macau "more circumspect."

Both of the main channels for getting cash out in Macau are being squeezed. UnionPay said in March that its payment network has tightened checks on suspicious transactions in the territory to combat money laundering.

Junkets are facing pressure from casinos and regulators to disclose the names of their customers.

Other methods of moving money are also disappearing. Jewelry counters on casino floors, where gamblers could do a quick buy-and-return transaction and come away with cash, have recently been shut.

"These outlets were put on these prime real-estate locations for one reason--to drive the mass business," said Ben Lee, managing partner of IGamiX Management and Consulting, who advises casinos. "Moving them away should thus have an inverse relationship to the growth of business there."

The biggest global impact of the crackdown will be felt in real estate. Chinese buyers have buoyed property markets from Sydney to Vancouver to London. Given the high prices of the homes involved, the buyers are certainly moving more than $50,000 out of the country.

One route favored by real-estate investors that has been shut down is a money-transfer service run by Bank of China Ltd. called You Hui Tong. Bank of China has said that it has received some regulatory approval for the service. China is also working on a deal with U.S. regulators that would force U.S. banks to disclose the assets of Chinese depositors.

The squeeze is already hitting Chinese developers working overseas, such as Country Garden Holdings Co. The developer has marketed some of the 10,000 units in a new waterfront land development in Danga Bay, Malaysia, to mainland buyers.

Country Garden's Malaysia project, its first international foray, was lauded as a success in its 2013 annual report, with contract sales of 7 billion yuan ($1.13 billion). But this year, it has suffered from cancellations, mainly from Chinese buyers, according to people close to the matter. Some have cited difficulty in obtaining mortgages or moving funds offshore as one of the reasons for canceling.

The company said in an emailed response that You Hui Tong isn't the only overseas remittance method its Chinese buyers use. Although the impact of the closing of the service is limited, it does affect its marketing campaign, the company said.

The developer is now trying to attract buyers through discounts. It is also offering customers advice on how to get the cash needed to buy a unit out of China. During a recent visit to its sales office, about a 10-minute drive from Singapore, a saleswoman said that with the Bank of China channel closed for now, clients should look into underground money-exchange channels.

Some Chinese are using friends' and family members' transfer quotas to get the money they need over the border. But that practice has raised red flags too, with global banks increasingly scrutinizing money laundering.

For those who seek government approvals for big property purchases abroad, various regulatory bodies in China are asking detailed questions about where the money comes from and what they are buying with it, said Darren Xia, China director at real-estate firm Jones Lang LaSalle. "The government isn't turning the tap off," Mr. Xia said. "But they don't want it to get out of control."

Write to Wei Gu at wei.gu@wsj.com

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