Two markets, one arbitrage opportunity. Talk of a pending deal at Sinopec Shanghai Petrochemical, an ethylene producer listed on the Hong Kong and domestic mainland stock exchanges, had investors racing to call their brokers. Mainland investors, though, were unable to act – trading in the Shanghai-listed A-shares was immediately suspended. Across the border, regulators took nearly an hour to halt trading, enough time for the shares to rise as much as 23 per cent.

Of course, there are plenty of anomalies in Greater China’s markets. Mainland investors are restricted to the domestic A-share markets, to which foreigners have only very limited access. The 30 companies with dual listings trade at an average discount of 35 per cent in Hong Kong relative to Shanghai, with some as much as 70 per cent cheaper.