HKEX executives, who were going ahead with the plan to raise £8 billion to fund the LSE purchase, had met shareholders in London and New York last month to gain support but were rebuffed.
Yields on two-year US Treasury yields fell as weakening data on manufacturing and the jobs market suggested the trade war with China has damaged the US economy.
The futures market was clearly expecting drastic action as it priced in a greater chance the Fed would have to cut rates by half a point at its September meeting
Beijing helped by fixing the yuan at a firmer level than many had feared, even though it was beyond 7 per dollar level for the first time since the global financial crisis.