There are other complicating factors. It is unclear, for example, how much marked-to-market gains are included in the reserves figure. But all in, the actual rate of reserves accumulation in the first quarter might be up to $100bn higher than the published number suggests. There is reason to be spooked by this. Rising hot money inflows, which are largely a bet on renminbi appreciation, show that Beijing's capital controls are inadequate. Already China's claims on the US equate to about one-third of China's gross domestic product, estimates economist Brad Setser. How much longer it can accumulate foreign assets to absorb inflows is questionable.

Second, the PBoC's accounts give some clues that further piles of foreign exchange are being parked at commercial banks. “Other foreign assets”, a line item on the central bank's accounts that has barely budged in four years, began rising in August last year. Anecdotal evidence suggests commercial banks may be meeting PBoC reserve requirements by accumulating foreign currency. Stone & McCarthy estimate that 75 per cent of the rise in reserve requirements may have been dollar denominated. On that basis, reserve hikes in January and March meant about $42.5bn further accumulation of foreign assets in the first quarter.