About 75 minutes after the start of dealing, London's FTSE 100 of leading shares stood at 6,155.
50 points, down 1.84 percent from Thursday's close.
In Frankfurt the DAX 30 tumbled by 1.
74 percent to 7,324.73 points and the Paris CAC 40 shed 1.
76 percent to 5,525.75.
The DJ Euro Stoxx 50 index of top eurozone shares slid 2.
04 percent to 4,188.01 points.
"It's that unnerving effect of the unknown which is spooking investors at the moment," said Henk Potts of Barclays Stockbrokers in London.
World equities had begun sliding on Thursday on renewed worries about the US subprime mortgage sector, which provides home loans to people with poor credit histories.
Leading indices in London, Frankfurt and Paris had each ended about 2.0 percent lower on Thursday.
Some investors and analysts fear that the US housing woes may eventually weaken global economic growth. Others see the current situation as temporary.
"The underlying picture still looks reasonably good in terms of economi