Firstly, it is making it more expensive to trade. The four main Chinese agricultural exchanges have raised their margins for futures dealing. Meanwhile, the Shanghai Futures Exchange, where the world's top three metals contracts are based, has pledged to increase margins for copper, aluminium, steel wire, gold and fuel oil to 10pc.

China has blamed US quantitative easing for increasing the amount of money sloshing around its economy. A first interest rate rise for three years hit global commodities hard in October.

Then, there has been a sell-off of central stockpiles, in an attempt to flood the market with more commodities and force down prices. Chinese authorities have sold corn, sugar and cotton from reserves this month, as well as putting on price controls. Cotton fell 9pc from its recent peaks this week.