The panicked mood prompted wild swings in Asian stock markets. Japan's Nikkei plummeted 7.6%. The Hang Seng in Hong Kong dropped 4.7%.
Investors turned to safe haven assets like the Japanese yen, which soared against the dollar. Gold jumped around 6%.
Markets in the U.K. will open Friday at 8 a.m. local time / 3 a.m. ET. London stock futures are trading around 7% down. U.S. stock futures are also lower.
British bank stocks traded in Hong Kong were hit especially hard -- HSBC fell more than 11%, and Standard Chartered nosedived more than 12%.
"The markets have been betting on remain in the past few days, and when the first results came in, that has reversed," said Vicky Pryce, an economist and former U.K. government official.
Cnn