Johannesburg - South Africa's rand slumped more than 8 percent against the dollar on Friday, on track to its biggest one-day percentage fall since 2008, as Britain voted to leave the European Union, knocking appetite for riskier assets.

At 06h40 GMT, the rand traded at 15.3400 versus the dollar, 6.53 percent weaker from its New York close on Thursday and its weakest level in three weeks, according to Thomson Reuters data.

The unit had earlier fallen to more than 8 percent to 15.6800 per dollar.

Government bonds also weakened, with the yield for the benchmark instrument due in 2026 adding 24 basis points to 9.12 percent, after jumping as much as 28.5 basis points earlier.

“Global risk appetite is being obliterated in the wake of the largest risk off event in recent times,” Nedbank Capital said in a note. “Markets are firmly in the grip of 'risk off', and caution is advised.”

Investors fret Brexit could spark anti-establishment movements in other European countries, some of which have already seen decline in traditional political parties.

Stocks were set to open lower at 07h00 GMT, with the JSE securities exchange's Top-40 futures index down nearly 5 percent.