China said on Monday it would spend about $3bn buying 1m tonnes of base metals, from aluminium to tin, in an effort to cushion its mining and smelting industry from plummeting demand and prices.

The announcement triggered a brief rally in the base metal sector in London and Shanghai, sending tin prices up to 10 per cent higher. But later prices dropped amid traders’ doubts about the plan and a new bout of gloom about prospects for the global economy.