China's trade surplus has widened to $US26.7 billion ($A25.85 billion) in August as exports rose and imports registered a surprise decline, amid recent signs of weakness in the world's second-largest economy.

Exports increased 2.7 per cent in August year-on-year to $US178 billion, the General Administration of Customs said in a statement on its website. Imports fell 2.6 per cent to $US151.3 billion.

The increase in exports in August outpaced the one per cent gain registered in July, but the decline in imports came as economists surveyed by Dow Jones Newswires had expected a 3.4 per cent rise.

China's economy has been struggling as a broader global slowdown and the European debt crisis has kept exports weak, while consumer spending at home lacks strength.

Gross domestic product in China, a key engine of the global economy, grew by 7.6 per cent in the second quarter through June, its worst performance in three years.

The government is targeting full-year growth of 7.5 per cent this year, though that is well below the 9.3 per cent recorded in 2011 and the 10.4 per cent in 2010.