The amount of China's yuan funds being used for foreign exchange saw a decline last month, official data shows.

The funds stood at 21.4084 trillion yuan (about 3.09 trillion US dollars) at the end of September, down from 21.5278 trillion yuan a month earlier, according to the People's Bank of China (PBOC), the country's central bank.

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

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

As a similar measure of capital flows, China's foreign exchange reserves stood at 3.087 trillion US dollars by the end of September, down 0.7 percent from a month ago.

The State Administration of Foreign Exchange said that although the external environment is still uncertain, the stable fundamentals of China's economy will provide a solid foundation for the steady operation of China's forex market.