The FTSE 100 Index has suffered its biggest one-day fall since 1987 after plummeting 10.9% to 5237.48 as coronavirus fears gripped the market.
Nearly £150 billion has been wiped off London's top index as markets.
On Thursday, the European Central Bank failed to calm markets as it announced measures to tackle Covid-19’s impact on the economy, but did not change interest rates.
On Wednesday, US President Donald Trump suspended travel from most of Europe to the US.
Spreadex analyst Connor Campbell said: "A horror show US open turned an already very bad day into the kind of session that could go down as historic, if for all the wrong reasons.
"It is hard to keep coming up with new metaphors for the scale of disaster facing the global markets.
"Equities are getting crushed under foot as investors flee to the fire exit, desperately scrambling about for safe havens that feel anything but."
He added: "The ECB's stimulus package seemingly only made matters worse.
"Withstanding the pressure to cut rates to a fresh record low, the central bank announced an 120 billion euro expansion to its ongoing quantitative easing programme, alongside new longer-term refinancing operations and cheap loans for banks to encourage lending to 'those affected most by the spread of the coronavirus'."
The news comes just days after more than £125 billion was lost from the FTSE 100 as markets were also hit by an oil price war between Saudi Arabia and Russia.
More than half a trillion pounds has been wiped off the FTSE100 index in less than three weeks, bringing the London market to its lowest level since 2012.
Coronavirus: Everything you need to know