For the past month or more, overnight interest rates in Hong Kong have been stuck just above zero per cent. Since everyone got used to ultra-low interest rates during the last couple of decades, it may not be immediately obvious how bizarre, unexpected and potentially alarming that situation is — or how it illustrates everything from the dwindling appetite of Asian investors for US assets, to a modest revival of Hong Kong’s capital markets, to surprising limits on the risk-taking capacity of banks and hedge funds.

Donald Trump’s gyrations on trade policy have not broken global financial markets just yet — but what is happening in Hong Kong shows they are feeling the strain.

The reason zero interest rates in Hong Kong are so odd is because its currency is pegged to the US dollar. That offers what seems like an easy arbitrage: borrow in Hong Kong at zero per cent, convert to dollars and earn US interest rates of more than 4 per cent. For an arbitrage, that is a large return, and since the currency is pegged the risk should be minimal. Yet for more than a month this divergence has continued. Every evening at seven o’clock the Hong Kong Monetary Authority announces the overnight rate. On Friday it stood, again, at 0.01 per cent.