China, once a magnet for global money, is now watching cash stream out.

Wealthy Chinese citizens are frequently moving cash secretly through a flourishing network of money-transfer agents. Chinese companies, for their part, are making big-ticket foreign acquisitions, buying up natural resources and letting foreign profits accumulate overseas.

China hasn’t reported on capital inflows and outflows since last year, but it is possible to gauge more recent flows using trade data, foreign-exchange reserves numbers released Saturday and other economic statistics. A Wall Street Journal analysis of that data suggests that in the 12 months through September, about $225 billion flowed out of China, equivalent to about 3% of the nation’s economic output last year.

China officially maintains a closed capital account, meaning it restricts the ability of individuals and businesses to move money across its borders. Chinese individuals aren’t allowed to move more than $50,000 per year out of the country. Chinese companies can exchange yuan for foreign currencies only for approved business purposes, such as paying for imports or approved foreign investments.

In reality, the closed system has become more porous and the rules are routinely ignored. “The wealthy in China have always had an open capital account,” says Eswar Prasad, a Cornell University economist and former International Monetary Fund official.

China’s $50,000-a-year limit on moving capital out presented a problem for him. He says he got around the restriction by recruiting friends to move chunks of his money under their own names. Real-estate agents in China say that is a common practice that is largely tolerated by authorities.

For years, China’s economy benefited from large flows of cash into the country from exports and from foreign investors. Incoming dollars were exchanged for yuan at China’s central bank, putting more yuan into the economy. That made it easier for banks to lend and companies to grow, but it also stoked inflation and contributed to real-estate and stock-market bubbles.

The outflow helps explain why China’s banks have been slow to increase lending this year. Accelerated outflows might force China’s central bank to push the yuan to appreciate more strongly against foreign currencies, to encourage Chinese investors to keep their money in the country.

In 1998, during the Asian financial crisis, Indonesia saw the equivalent of 23% of its annual economic output leave the country—far higher than the 3% estimated to have exited China over the recent 12-month period. China’s economy is protected from such catastrophic outflows by its restrictions on capital movement and by its substantial foreign-currency reserves, currently $3.29 trillion.

The Journal’s $225 billion estimate for the year ended in September captures both legal capital outflow and some of the illicit flow. Several economists also have attempted to calculate outflow. Charles Dumas, an economist at Lombard Street Research, estimated net outflows of $300 billion over the same period.

One factor contributing to the reduced reserves is that Chinese exporters are keeping more of the money they make abroad in dollars, rather than converting it to yuan, economists say.

Because the $225 billion figure is derived from broad economic statistics, it is impossible to say how much of the outflow is legitimate personal and corporate transactions and how much was moved illegally or was the product of illegal activities.

A sprawling industry has developed to help Chinese get money out. Services range from the money-transfer agents to private jets that ferry money by customs officials unmolested, according to lawyers and brokers who help Chinese investors find investments abroad. Sometimes bank transfers by companies hide personal money being moved out, these people say. Another method is to piggyback personal cash atop legitimate export and import transactions, at times by using fake invoices, they say. People even carry bags of cash across the border.

Hong Kong, although part of China, has a separate financial system and currency—and no restrictions on outbound capital. Consequently, there are restrictions on mainland Chinese moving money to Hong Kong.

One legal way that some elite Chinese have gotten money offshore is by taking their companies public in Hong Kong, then selling shares.

Macau, like Hong Kong, is part of China but has its own financial system, and mainlanders face the same restrictions on moving money there. Gamblers frequently use the services of local “money lenders” in Macao, and subsequently need money to pay off their casino debts. The problem is getting it out of China.

Some punters use their company structures to transfer cash into accounts set up by associates elsewhere in China, claiming the transactions were for approved purchases. Then equivalent amounts in Hong Kong dollars would be deposited into separate accounts belonging to the entities that had lent the punters the gambling money.

“No funds actually cross the border, so this method is difficult to detect and impossible to measure,” says Stephen Green, head of China research at Standard Chartered Bank, who has studied Chinese money flows.

Its all part of the ‘brave new world’.