An unconfirmed blockade on key iron ore shipments has wiped more than $5 billion from mining giant BHP's value, but experts say tough talk from China's steelmakers was apolitical and nothing new.

Beijing's state iron ore buyer has told steelmakers to pause imports of BHP ore, amid hardball negotiations over the price of the crucial resource, Bloomberg reported on Tuesday.

The news prompted a 2.5 per cent sell-off in BHP shares, wiping more than $5 billion from the world's biggest miner's $216 billion market cap.

The federal opposition has called for the Commonwealth to step in to support BHP and Australian iron ore producers.

"We need a prime minister who stands up for Australia when it comes to these negotiations," defence spokesman Angus Taylor told Sky News.

"It's going back to the

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