BEIJING, Sept. 9 (Xinhua) -- China's industrial output and fixed-asset investment continued to weaken in August while retail sales picked up slightly, official data showed Sunday.

The country's industrial value-added output expanded 8.9 percent year-on-year in August, down from a 9.2 percent growth in July and and the slowest since May 2009, according to figures from the National Bureau of Statistics (NBS).

Urban fixed-asset investment increased 20.2 percent year-on-year to 21.8 trillion yuan (3.4 trillion U.S. dollars) in the first eight months of the year, 0.2 percentage points slower than the growth of the Jan.-July period.

Retail sales rose 13.2 percent year-on-year in August, 0.1 percentage points higher than the growth rate in July.

"China's economy is still in the trough and this situation is likely to go on longer than expected," said Liu Yuanchun, deputy head of the School of Economics at the Renmin University of China.

During the Jan.-Aug. period, real estate investment expanded 15.6 percent year-on-year to 4.4 trillion yuan, accelerating by 0.2 percentage points from the Jan.-July level, the NBS said.

Private fixed-asset investment went up 25.1 percent to 13.5 trillion yuan, down 0.4 percentage points from the Jan.-July period.