Chinese efforts to open domestic bond markets have attracted the attention of American hedge funds searching for a new source of investment returns.

Hedge funds have long been able to invest in Chinese stocks through American and Hong Kong-based stock exchanges. A select group, including Bridgewater Associates and Man Group, has even gained permission to offer hedge funds trading Chinese assets to the country’s wealthy residents and large investors.

But the Chinese government’s new “Bond Connect” program has sparked what may be the fastest-growing area of interest in the country for foreign asset managers.

Since starting the program last year, Chinese authorities have granted access to funds managed by Bridgewater Associates, Castle Hook Partners, Key Square Capital Management, Light Sky Macro, Nokota Management and Paloma Partners, according to a list of investors maintained by the Bond Connect. The program allows the funds to more readily trade Chinese asset-backed securities, corporate bonds and government debt instruments through Hong Kong exchanges.

The $5 billion Asian hedge fund Graticule Asset Management has also discussed gaining access to the Chinese bond market, viewing it as the next frontier of macroeconomic investing, said a person who was pitched on the idea.

Key Square, Light Sky and Paloma declined to comment through a spokesperson. The other firms did not reply with comment in time for publication.

Hedge funds and other asset managers can invest in Chinese government bonds through indexes tracking the country’s debt, and Bloomberg has said it will add Chinese bonds to the Bloomberg Barclays Global Aggregate Index next year, making it the first global bond index to include a broad swath of the country’s debt.

The Bond Connect, however, allows an unprecedented level of access to Chinese bond trading for hedge funds and other short-term speculators. Investors say there are still complicating factors, such as the government’s control of markets, limits on large trades and a dearth of hedging options.

“While the initiative has its limitations, we expect these to be reduced or eliminated over time,” Lazard Asset Management’s emerging markets debt team wrote in a note last month. “We believe investors should prepare now for the continued evolution of Chinese debt markets by seeking access to Bond Connect.”

China started the Bond Connect program last year to attract medium- and long-term investors to its debt market, which has ballooned to the third-largest in the world following an extended economic expansion.

Hedge funds typically hold securities for shorter time periods, attempting to profit from price dislocations. Foreign investors have primarily used the access to trade Chinese bank notes and short-term government debt, according to data maintained by the Chinese government.

The Bond Connect said in a statement that it has full discretion to approve investors and that U.S. hedge funds “are complying with the market rules and requirements.”

Bridgewater has begun to invest in Chinese debt through its more than $50 billion All Weather strategy, which balances investments in bonds, stocks and commodities, a person familiar with the matter said. The firm also has plans to start a version of the strategy that exclusively trades Chinese asset and will be offered to mainland investors.

The firm, led by Ray Dalio, has long courted the Chinese government in hopes of eventually profiting from the country’s economic growth. In a March interview with the Chinese business magazine Caixin, Dalio said restructuring China’s growing debt levels “requires thoughtfulness.”

“The question is not just how to deal with debt that has been accumulated, but also the flow of credit and curtailing spending and would that decline in spending be too traumatic to bear,” Dalio said.

Bridgewater’s charm offensive has raised questions about the objectivity of its research and investment disclosures. The firm lists Chinese holdings under a broad, non-Japan Asia category in investment reports, which differs from its practice of disclosing individual country exposures, the person familiar with its operations said.

A high-volatility version of All Weather was in the red for the year through April after making double-digit returns last year, according to Absolute Return data.

George Soros has also received approval to directly trade Chinese bonds through an entity called the “Quantum China Fund” that is associated with his private investment office, a person familiar with the matter said. Key Square, founded by Soros’ former top deputy Scott Bessent, was approved as an external manager for the fund, the person said.

Key Square has also been granted the ability to trade Chinese bonds through its hedge funds. The firm’s main fund gained about 7% through April after losing more than 7% last year, a person familiar with the matter said.

Soros declined to comment on the Chinese bond market through a spokesperson. But he has raised concerns about China’s debt in recent years, saying at the 2016 World Economic Forum in Davos that it could lead to a financial crisis.

A string of recent defaults by Chinese companies on their high-yield debt has revived fears that tightening credit conditions could lead to distress in the country’s corporate sector.

The run-up in credit has drawn concerns from Robert Gibbins’ Autonomy Capital, which manages more than $5 billion in developed and emerging market investments. Autonomy said in a February letter to investors it anticipates China’s economy entering a “slowdown” that could depress bond yields.

“We see current yields appropriately pricing negative factors for Chinese bonds,” Autonomy wrote. “While we expect financial regulations to stay tight, in our view they will not prevent bond yields from ultimately reflecting China’s weakening economic fundamentals. We believe a cyclical slowdown is hard to avoid and may open the door for monetary easing at a later stage.”

A spokesperson for Autonomy declined to comment on whether the firm plans to invest in Chinese debt through the Bond Connect program.