The ranks of China’s wealthy continue to surge. As their economy shows signs of weakness at home, they’re sending money overseas at unprecedented levels to seek safer investments — often in violation of currency controls meant to keep money inside China. ... The methods include China’s underground banks, transfers using Hong Kong money changers, carrying cash over borders and pooling the quotas of family and friends — a practice known as “smurfing.” The transfers exist in a gray area of cross-border legality: What’s perfectly legitimate in another country can contravene the law in China. ... In Hong Kong, more than 1,200 currency-exchange shops have seemingly little daily activity. These brightly lit storefronts specialize in helping wealthy Chinese transfer their money overseas. The premium isn’t high — only about 1,000 yuan ($160) per HK$1 million ($130,000) more than bank exchange rates would be if they could do the transaction. ... It works like this: Chinese come to Hong Kong and open a bank account. Then they go to a money-change shop, which provides a mainland bank account number for the customer to make a domestic transfer from his or her account inside China. As soon as that transaction is confirmed, typically in just two hours, the Hong Kong money changer then transfers the equivalent in Hong Kong or U.S. dollars or any other foreign currency into the client’s Hong Kong account. Technically, no money crosses the border -- both transactions are completed by domestic transfers. ... While the first exchange has to be set up face-to-face, customers can place future orders via instant-messaging services such as WhatsApp or WeChat, and money changers set no limit on how much money they can move.