China's foreign exchange reserves are so vast that the numbers barely register. Yet in just six months the reserve pile has jumped another $318bn (€213bn, £195bn), a sum nearly equal to the annual gross domestic product of Argentina.

With a grand total of $2,270bn, that is a lot of insurance against financial crises but, as China has discovered this year, such reserves are also a trap, especially when two-thirds are in vulnerable US dollar assets.