China's foreign trade in August dropped 9.7 percent year on year to 2.04 trillion yuan (320.8 billion U.S. dollars), a steeper decline than the 8.8 percent contraction in July, official data showed on Tuesday.

Exports fell 6.1 percent year on year to 1.2 trillion yuan, compared with an 8.9-percent drop in July, while imports slumped 14.3 percent to 836.1 billion yuan, compared with July's decrease of 8.6 percent, according to the General Administration of Customs (GAC).

Trade surplus expanded by 20.1 percent to 368 billion yuan in August.

In the first eight months of 2015, foreign trade slipped 7.7 percent year on year to 15.67 trillion yuan, the GAC figures showed.

Exports dipped 1.6 percent to 8.95 trillion yuan in the Jan.-Aug. period, while imports fell 14.6 percent to 6.72 trillion yuan.

In the first eight months, trade surplus jumped 80.8 percent to 2.23 trillion yuan, according to the GAC.

Export of steel grew 26.5 percent year on year to reach 71.9 million tonnes in the first eight months while iron ore imports slipped 0.2 percent to stand at 613 million tonnes.

China imported 139 million tonnes of coal from Jan.-Aug., down 31.3 percent year on year while imports of refined oil and crude oil increased 4.1 percent and 9.8 percent year on year respectively in the period.

Qu Hongbin, chief China economist at HSBC, attributed the slump in export growth mainly to sluggish external demand, especially exports to the European Union (EU) and Japan.

Trade with the EU, China's largest trade partner, slipped 8.4 percent year on year in the first eight months to 2.27 trillion yuan, with exports dropping by 4.9 percent to 1.41 trillion yuan and imports plunging by 13.7 percent to 859.87 billion yuan.

Trade with fifth-largest partner, Japan, fell 11.1 percent to 1.11 trillion yuan, with exports and imports dropping by 10.5 percent and 11.6 percent respectively.

However, trade with the United States and the Association of Southeast Asian Nations, China's second- and third-largest trade partners, managed to climb by 2 percent and 0.4 percent to reach 2.22 trillion yuan and 1.86 trillion yuan respectively, driven by increased exports to those countries.