BEIJING — China’s yuan funds outstanding for foreign exchange dropped for an ninth straight month in April, central bank data showed on May 14.

The funds stood at 21.25 trillion yuan (about $3.17 trillion) at the end of last month, falling 861 million yuan from March, according to the People’s Bank of China, the central bank.

As the Chinese yuan is not freely convertible under the capital account, the central bank has to purchase foreign currency generated by trade surplus and foreign investment in the country, adding funds to the money market.

Such funds are an important indicator of cross-border foreign capital flows and domestic yuan liquidity.

A similar measure of capital flow, the country’s foreign exchange reserves fell to $3.094 trillion at the end of April, compared with $3.098 trillion at the end of March, according to the State Administration of Foreign Exchange.