Chinese imports slumped by nearly 18 percent year-on-year in September, Customs said on Tuesday, in the latest poor figures from the world's second-largest economy.

The Asian giant is the world's leading trader in goods but its slowing economic growth has seen prices plunge for the commodities it uses, sending turmoil through producer countries such as Australia.

Imports fell to 924 billion yuan (around $146 billion), Customs said in a statement.

"Imports of some of the bulk commodity exhibited an increase in volume and a fall in price," Customs spokesman Huang Songping told reporters.

The country has also been hit by falling demand in some key markets for its manufactured goods, and September exports slipped by 1.1 percent to 1.30 trillion yuan, Customs said.

"There remain some obstacles facing China's foreign trade growth," Huang said, adding that the monthly export decline had narrowed.

The trade surplus for the month nearly doubled to 376.2 billion yuan.