China's forex reserves fell for a third straight month in September and by slightly more than markets expected. That's according to data out Friday from the central bank.

Forex reserves fell to $3.166 trillion from $3.185 trillion in August. Traders believe the central bank has stepped in since July to prop up the yuan, which has weakened 2.7 percent against the U.S. dollar so far this year.

At the same time, capital outflows, and the seasonal factor of tourists’ surging demand for foreign currencies during the National Day holiday, also contributed to the shrinking pool of forex reserves.