So the loans are often made off the balance sheet, and therefore outside the purview of bank regulators, which is why experts call it shadow banking. They are made at higher interest rates, so everyone wins — the borrower, the banks and the investor of the wealth management product — as long as the borrower repays.

“The banks now have these dark pools of money,” said Joe Zhang, a former investment banker and the author of “Inside China’s Shadow Banking: The Next Subprime Crisis?” He said, “To finance deals they usually have a trust company stand in the middle and simply put their stamp on it. The trust companies get a fee for that but often they do next to nothing. The bank does all the work.”

The explosive growth of wealth management products began about five years ago, enticing Chinese banks, big and small, to engage in shadow banking.

By the end of last year, China’s shadow banking activity was valued at $6 trillion, twice the level in 2010, and now equal to 69 percent of China’s gross domestic product, according to a report released in May by JPMorgan Chase. Now, even state-run banks are doing shadow lending, extending financing to companies in high-risk sectors.

Who is responsible for the loans is not always clear, and that’s where everyone starts getting nervous.

“If a wealth management product defaults, who is on the hook?” asked Michael Pettis, a finance professor at Peking University in Beijing and senior associate at the Carnegie Endowment for International Peace. “It’s all very murky. In these things, the banks are technically acting as intermediaries.”

Financial experts worry about the lack of transparency in the market when China’s economy is weakening. They also fret about whether some borrowers have the cash flow to repay their loans.