These 3 triggers could cause 50% crash: Economist

Greek default is 'a given': Economist

Greece, China and a rate hike from the Federal Reserve are looming over the global investment community and could lead to a plunge of around 50 percent for stock markets, according to one economist.

Charles Robertson, global chief economist at Renaissance Capital, stressed on Thursday that the global economy remained fragile, seven years after the financial crash of 2008.

"We're seeing just how fragile it is with that Greek crisis right now. The second risk was China - that's always a possible problem which could provoke something much worse. The third is something along the lines of a Fed (rate) hike," he said.

This latter factor has "more unexpected consequences than people assume ahead of time," Robertson added.

He first made his prediction of a 50 percent stock market crash in January 2015, arguing that historical evidence implied the would begin a slow decline this year. The index is currently around 2,046 points, but Robertson expects it to collapse to 1,100 points in March 2016, with the U.S. falling into a recession.

Traders work on the floor of the New York Stock Exchange.
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However, he did say that if equity markets dropped by half, it would present a "massive buying opportunity."

The S&P 500 is down 0.6 percent year-to-date and all global markets - especially China - have seen some hefty bouts of volatility over recent weeks. Despite this, not all market participants are as bearish on stocks as Robertson.

"Investors should resist the urge to cash in their stock market investments, provided they are still in it for the long term," Laith Khalaf, a senior analyst at Hargreaves Lansdown, said in a research note this week.

"If you sell up every time there is bad news out there, and buy back in when things look rosier, you're probably going to lose out in the process."

Jim McCaughan, CEO of asset management group Principal Global Investors, was another who said he was watching global markets carefully for buying opportunities.

"Excess liquidity in a closed system has caused extreme volatility (in China). (Chinese stocks are) not yet cheap, so still a dangerous market. But continue to buy U.S. equities on setbacks," he told CNBC via email.