Slumping prices saved China more than $160 billion on its imports of commodities such as oil, iron ore, coal and copper last year, official figures showed on Wednesday.

Slowing growth in the world's second-largest economy has hammered global raw materials prices, sending shockwaves through resource-rich producer countries from Australia to Zambia.

But the falls have proved a boon to China itself, which is reportedly taking advantage of the low costs to stockpile oil.

The average price of China's oil imports plummeted 45.3 percent in 2015 on the previous year, Customs spokesman Huang Songping said, with volumes rising 8.8 percent to 335.5 million tonnes according to the Customs website.

Overall, the country spent $134.5 billion on crude oil imports during the year.

The quantity it bought was a record, Bloomberg News reported, saying it has eased rules to let private refiners import crude, while boosting shipments to fill national stockpiles.

Iron ore imports were up 2.2 percent by volume and totalled $57.6 billion by value -- but on average cost 39 percent less than in 2014.

Copper imports were flat by quantity but 17.1 percent cheaper per tonne, with a total of $19.2 billion-worth brought in.

Coal prices also dropped 21.8 percent, with volumes of the fuel also slumping, by 29.9 percent.

Demand for some materials has weakened in the Asian giant due to manufacturing overcapacity and a cooling property market.

Calculations by AFP show that for the four commodities in total, the quantities imported would have cost $160.5 billion more at 2014's average prices.

For crude oil alone, the saving amounted to $113.9 billion.

Overall, China's import prices declined by 11.6 percent on average in 2015, while prices of exports edged down just one percent, Huang said.

"The price conditions for China's trade improved sharply and the efficiency of foreign trade increased," he told reporters.

For the full year, China's imports slumped 14.1 percent by value on 2014 to $1.68 trillion, Customs said, while exports were down 2.8 percent to $2.28 trillion.

"The sharp falls in global commodity prices and the slowdown in commodity import volume growth are the main causes for the decrease in China's 2015 import value," Huang said.

Beijing is seeking to transition the country's growth model away from reliance on exports and fixed-asset investment towards a consumer-driven economy, but the reform is proving bumpy.

China logged its worst economic performance since the global financial crisis in the third quarter of 2015, with gross domestic product (GDP) rising just 6.9 percent -- its lowest level in six years.

GDP figures for the full year are due to be released next week.