The rest of the year, it's a struggle to defeat capital controls.

Authorities complain of 'leaks' in system and demand reporting of large deals.

China has tightened checks on citizens exchanging foreign currency in anticipation of renewed downward pressure on the renminbi in the new year.

Banks have been asked to improve standards for verifying customers' identities and to report "large or questionable transactions", the State Administration of Foreign Exchange (Safe) said in a public statement at the weekend.

"There have been leaks in China's system of personal foreign exchange purchases," the statement said, giving as an example the way individuals and companies avoid capital controls on overseas investments by disguising their transactions as goods purchases.