Net sales of foreign currency by China's central bank and financial institutions accelerated last month, suggesting capital outflows picked up as the nation's economic slowdown deepened.

Yuan positions at financial institutions accumulated from foreign exchange purchases fell 17.4 billion yuan ($2.75 billion) to 25.64 trillion yuan at the end of August from 25.658 trillion yuan in July, the People's Bank of China said on Tuesday. That compares with net sales of 3.82 billion yuan in July.

The report follows data showing foreign investment in China fell in July to the lowest level in two years amid signs economic expansion may decelerate for a seventh quarter. At the same time, the US Federal Reserve's decision last week to buy mortgage debt in a third round of so-called quantitative easing may increase investors' appetite for yuan assets, said Joy Yang, a former International Monetary Fund economist.

"Capital outflow risks are moderate for China as long as it has the monetary tools to neutralize the impact," said Yang, now chief Greater China economist at Mirae Asset Securities (HK) Ltd in Hong Kong. Outflows are "tiny compared to China's $3 trillion foreign-exchange reserves," she said.