Shares have tumbled after US President Donald Trump restricted travel to the US from mainland Europe in a bid to slow the spread of the coronavirus.
London's FTSE 100 index sank more than 5 percent, with similar declines seen in other European markets.
Stocks in Asia saw big falls, with Japan's benchmark Nikkei 225 index closing 4.4 percent lower. It followed steep losses in US shares on Wednesday, with the Dow Jones plunging by 5.8 percent.
John Authers is the senior markets editor at Bloomberg based in New York.
He speaks to Susie Ferguson.