Global stocks fell on Friday.
The MSCI world index sank 1.5 percent, its biggest drop since 8 February.
The S&P 500 fell 0.9 percent, its biggest drop in three weeks.
The STOXX Europe 600 plunged 2.4 percent, its third consecutive decline.
The US 10-year Treasury note yield fell as much as six basis points to 1.63 percent, the lowest on a closing basis since December 2012. German 10-year bund yields fell to an all-time low of 0.01 percent.
West Texas Intermediate crude plunged 3 percent.
Sterling fell as much as 1.9 percent against the dollar, the largest drop since October 2009, after a poll showed 55 percent in the UK wanted to leave the EU while 45 percent wanted to remain.