SINGAPORE - China's foreign exchange reforms have made "significant progress," though the impact will be seen over time, Beijing's central bank governor told fellow financial leaders on Tuesday.

The remarks by the governor of the People's Bank of China, Zhou Xiaochuan, came amid calls from other delegates to the annual meeting of the IMF and World Bank for more action to ensure flexibility in currency rates.

"Significant progress has been made to improve the exchange regime to allow greater flexibility," Zhou said of China's controls on its currency, the yuan, which Beijing says are needed to protect its developing economy. "The impact of these policies will be felt over time."

A US official meanwhile urged the International Monetary Fund, which seeks to promote financial stability and provides loans to countries in crisis, to step up its oversight of currency issues.

"The encouragement of appropriate exchange rate policies to facilitate international trade and global growth remain the IMF's most fundamental responsibilities," said the US Treasury assistant secretary for international affairs, Clay Lowery.

"This entails rigorous assessments of members' exchange-rate regimes," Lowery said, warning that ceding that role would result in countries taking action independently, "frankly to the detriment of us all," he said.

Lowry's comments came as US Treasury Secretary Henry Paulson arrived in China for a visit expected to include talks on Washington's appeals for a stronger Chinese currency.

IMF President Rodrigo de Rato acknowledged the calls for more surveillance over currency issues.

"The responsibility of the IMF is very clear. We are, we have a mandate to macroeconomic and financial stability," de Rato said, adding that "exchange rates form part of that mandate."

But such discussions are not done in public, he said.

"At the same time, as it is known, the discussion of exchange rate equilibrium positions is held in a discreet way because it is very sensitive information sometimes," he said.