Investment banks are dusting off models from the 2008 financial crisis to gauge the right time to buy back into stock markets that have plunged 30 per cent from their February record highs because of the coronavirus crisis.

That inflection point is not easy to model when the virus is still spreading rapidly across Europe and the United States.

But the US government's $2 trillion in fiscal stimulus, coming on top of unprecedented measures from the US Federal Reserve and other central banks on Tuesday triggered one of the sharpest global equity market rallies in decades.

Wall Street's so-called fear gauge, the Cboe Volatility Index has also fallen from its highs.

For some, the signals for a reversal are in place.

Veteran investor Bill Ackman told investors in his listed Pershing fund he had turned increasingly positive on stocks and credit.