Australian shares had their worst session since February losing more than 2 per cent on Monday as the price of iron ore traded in the futures market sank to $US90 a tonne, extending the collapse of the economy's top export to more than 60 per cent from its May peak.

The relentless pace of iron ore’s decline has strategists at a loss as to when producers might see a reprieve, inflicting further pain on the major miners which fell by more than 3 per cent on the ASX, and the national accounts.