A rush of coronavirus cases outside China wiped nearly $474 billion off the value of European stock markets today.
Investors have been assessing the likely impact of the outbreak turning into a pandemic.
A 5.4% slump saw Milan shares marking their worst day since mid-2016, as Italy reported the biggest flare-up of the virus in Europe with at least six deaths and more than 200 infections, which is likely to further upset the country's already ailing economy.
The pan-European STOXX 600 dropped 3.8%, posting its biggest intra-day percentage slump since Britain voted to exit the European Union in June 2016.
A surge in infections in South Korea and Iran prompted widespread moves out of equities and into safe havens.
"Today signifies that markets did not expect this to become a major issue outside of China," said Craig Erlam, a senior market analyst at Oanda. "Investors are going to be far more sensitive now."
"Arguably (there's been) an element of complacency over the course of last month because there's just been a general belief that it will get better - this kind of mentality has not helped."
Both European and US stock markets have been on a decade-long bull run since the financial crisis, and the benchmark European index was trading at record highs as recently as last Wednesday, confident that the outbreak's impact would be limited to China.
Airlines were among the worst performers on the STOXX 600, with EasyJet, Ryanair, Air France and Lufthansa down between 7.4% and 12.6%.
Europe's travel and leisure index tumbled 6% and was the weakest regional sector.
Broad-based declines on the index sent luxury goods makers, miners, automakers, chipmakers and banking shares - which alltend to be tightly sensitive to expectations of global growth - down between 4% and 6%.
Fears of the economic impact from the outbreak bolstered expectations - already at 50% - that the European Central Bank will cut interest rates by 10 basis points in July.
German shares fell 4%, shrugging off an Ifo survey that showed business morale rose unexpectedly in February.
Juventus slumped 11.8% after the Serie A leader posted a net loss of 50.3 million euros in the first half, compared to a profit a year earlier.
Bank of Ireland fell 5% after its underlying pretax profit fell for the fourth successive year and the lender added it would take longer than forecast to hit a return ontangible equity (ROTE) above 10%.
The overall ISEQ index in Dublin was down over 4% at the close of business this evening.