(This version of the story corrects the date of remarks by Fed's Kaplan to July 14 in paragraph 14)

By Marius Zaharia

HONG KONG (Reuters) - In September 2015, the U.S. Federal Reserve cited risks from China as a key reason for delaying its first interest rate hike in a decade. A wall of Chinese debt maturing in the next few years could jolt the country back into the U.S. central bank's policy deliberations.

Two years ago, it was a collapse in Chinese stocks, a surprise yuan devaluation and shrinking foreign exchange reserves that roiled financial markets that delayed the Fed, but it did raise rates three months later and has tightened further since.

Now, some see risks emerging in China's dollar-denominated bonds that could give the Fed greater pause for thought as it raises rates, even as other central banks signal a shift from ultra-easy policy.

To be sure, Fed officials have not publicly flagged China's debt as a major risk in their policy discussions. However, debt analysts point to the possibility of another September 2015 moment in which the Fed takes its cues from concerns about China.

"Back then, I said that U.S. monetary policy is not made in Washington, it's made in Beijing," said Joachim Fels, global economic advisor at bond giant PIMCO.

"China does have a major impact on monetary policies elsewhere ... This year has been smooth sailing for global central banks because there were no shockwaves from China but I expect that to change if we think beyond the next few months."

The outstanding amount of dollar bonds issued by Chinese entities has grown almost 20 times since the 2008-09 global financial crisis to just over half a trillion dollars, according to data from the Bank for International Settlements. Since September 2015, it has grown almost 50 percent.

China's dollar bonds are now almost a third of the emerging market total dollar issuance, up from a quarter in September 2015 and less than 5 percent before the Fed first began printing money in December 2008.

A fifth of China's dollar bonds mature within a year, according to BIS data. More than half are due in the next five, Thomson Reuters data show.

If U.S. borrowing costs start rising as a result of the Fed's exit from its unconventional monetary policy, that debt would have to be rolled over at higher costs, chipping away at the real economy in China.

Alternatively, Chinese companies might decide to refinance their debt in local currency, creating weakening pressure on the yuan.

Either development would reverberate globally and create a major external challenge for Fed policy.