BEIJING — China's yuan funds, outstanding for foreign exchange, continued to decline in May, central bank data showed on June 15.

The funds stood at 21.18 trillion yuan (about $2.99 trillion) at the end of last month, down by 11.22 billion yuan from April, according to the People's Bank of China.

As the Chinese yuan is not freely convertible under the capital account, the central bank has to purchase foreign currency generated by a 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.

The foreign exchange reserves expanded to $3.1017 trillion at the end of May, from $3.0915 trillion at the end of April, official data recently showed.