China's foreign exchange watchdog said Monday that the surplus of Chinese banks' foreign exchange from bank-to-client transactions reached $273.7 billion in the first half of 2011.

During the period, institutional and individual clients sold $788.2 billion in foreign exchange to banks while purchasing $514.4 billion , the State Administration of Foreign Exchange (SAFE) said in an online statement.

More foreign currencies were sold than bought through Chinese banks over the May-to-June period as the yuan continued to appreciate, resulting in $43 billion of foreign exchange surplus in June compared with $51.9 billion in May, the statement said.

In June, institutional and individual clients exchanged $143.6 billion in foreign currencies through banks and purchased $100.5 billion, it said.

The banks received $217.7 billion of overseas business-related proceeds in June and paid $174 billion for their clients during the period, leaving a surplus of $43.7 billion, the statement noted.

In the first half of the year, overseas business-related proceeds from the banks' clients totaled $1.09 trillion while payments stood at $916.6 billion , resulting a surplus of $177 billion, it added.

Foreign exchange surpluses, which make up part of the country's foreign exchange reserves together with current account surpluses and foreign direct investment inflow, do not include banks' own foreign exchange transactions or interbank transactions, according to SAFE.

Last year, foreign exchange surpluses created through Chinese banks' transactions with domestic clients increased 51 percent year-on-year to reach $397.7 billion, the SAFE data showed.