China's iron ore imports slumped 8.5 per cent by volume in May from a year earlier, threatening Australia's surprisingly good first-quarter gross domestic product growth which was helped by earlier strong exports of the key steelmaking commodity to China.

Data released by the Customs Bureau on Monday showed in May China's overall balance of trade fell 10 per cent from a year earlier, after another weak month of imports.

The sluggish overall trade performance came despite surging exports to the United States, which grew 7.8 per cent from a year earlier.

"We expect China's headline trade growth to gradually recover over the coming quarters," said Julian Evans-Pritchard, an economist with Capital Economics in Singapore.

China's iron ore imports had fluctuated this year as construction activity remained subdued and despite the housing market showing sign of stabilising after a year-long slump.

The official data showed China imported 71 million tonnes of iron ore in May, down 12 per cent from the previous month. The figure was significantly weaker than the 77 million tonnes imported in May last year and 9 per cent below the average monthly volume for 2014.

While Beijing did not break out commodity imports by country, Australia accounted for about 60 per cent of China's imported iron ore.

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