The pound slumped to its lowest in more than three decades on Friday as results on Britain's vote on European Union membership give the "leave" side a small but growing lead.

The currency tumbled to as low as $1.3460 on Friday, which was its lowest level in 31 years.

It fell about 10 percent from the 2016 high of $1.50 hit just hours earlier.

Uncertainty over the vote's outcome has kept world currency markets on edge.

The yen, meanwhile, strengthened as investors sought safety in the currency, which is considered a haven.