BEIJING -- China's foreign exchange watchdog said Thursday that the surplus of Chinese banks' foreign exchange purchases to sales in client transactions increased 51 percent through 2010 to stand at $397.7 billion at year-end.

China's institutional and individual clients sold $1.33 trillion in foreign exchange to banks in 2010 while purchasing $932.7 billion, said the State Administration of Foreign Exchange (SAFE) in an online statement.

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In 2009, the annual surplus fell 42 percent to $263.5 billion, according to SAFE's data released in March 2010.

The statement noted the figures did not include banks' own forex transactions and interbank transactions.

The forex surplus in December 2010 totaled $51.5 billion, as clients sold $146.2 billion of foreign exchange, up 13 percent from November, while purchasing $94.7 billion, up 12 percent, it said.

Chinese banks received $1.89 trillion for their clients in overseas business in 2010 and paid $1.59 trillion to overseas business, it added.

The SAFE only began releasing monthly and quarterly data on bank foreign exchange transactions in 2010.