A top official at China's central bank said Monday uncertainties remained about when Beijing would allow the yuan to appreciate, and it would depend on domestic and global economic conditions.

At the weekend, central bank governor Zhou Xiaochuan hinted the policy of effectively pegging the yuan to the US dollar -- in place since mid-2008 -- could change, saying it was temporary and would be withdrawn "sooner or later".

China's currency policy has riled Beijing's trade partners in the United States and the European Union, who say the yuan is undervalued to boost Chinese exports.

"We need to consolidate the economic recovery ... there are still many uncertainties," People's Bank of China vice governor Su Ning told reporters on the sidelines of the nation's annual session of parliament.

"We will seriously study the economic situation inside and outside the country to decide when it would be appropriate."

On Saturday, Zhou defended the controversial exchange rate policy, saying it was "extraordinary" and that the timing of a return to "normal" policies was a complex issue.

"Although we have seen signs of recovery, the impact of the financial crisis is still very keenly felt," Zhou said.

"Sooner or later we will withdraw economic stimulus policies (but) we need to be cautious about choosing the timing of the exit... including (from) the yuan exchange rate policy."

China has said maintaining a stable currency is a "top priority" and is needed for the survival of Chinese companies and jobs growth in the world's third-largest economy, as export markets slowly recover from the global crisis.

But as the nation powers out of the crisis -- its economy grew by 10.7 percent in the fourth quarter of 2009 after a massive public spending programme -- there is a growing clamour for the yuan to appreciate.