Iron ore prices have plunged to a fresh six-year low as the commodity gets caught up in the fallout from China’s massive sharemarket plunge.

The falls came after China plummeted more than 10 per cent to $US44.59 a tonne on Wednesday night, their lowest level since 2009.

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At that price, most Australian miners would be producing at a loss, with the exception of low-cost giants Rio Tinto and BHP Billiton.

Miners have already been under pressure on the stock market: Fortescue Metals slumped more than six per cent on Wednesday, while BHP and Rio each lost more than three per cent.

Iron ore prices hit a low of $US47 a tonne in April this year before recovering to rise above $US64 a tonne in June.

The slide in iron ore comes as China’s share market remains in freefall, even in the face of the government’s extraordinary efforts to calm investors.

China has suspended trading in more than half of the country’s listed stocks, banned short selling and new listings, and enlisted the help of the major stock brokers through a 120 billion yuan ($A26 billion) stabilisation fund.

But the moves have so far failed to stop the bleeding and the Shanghai Composite Index, which has lost more than 30 per cent in less than a month, dived another 5.9 per cent on Wednesday.