Analysts said large institutions placed big bets, having hired top polling firms to measure sentiment ahead of Thursday's referendum.
Sterling hit a 2016 high and the euro surged against the dollar and yen on Thursday after a series of late opinion polls favored Britain staying in the European Union and bookmakers' odds indicated a further shift towards the "remain" camp.
Analysts said large institutions placed big bets, having hired top polling firms to measure sentiment ahead of Thursday's referendum. Results are not expected until after the close of U.S. trading that day, but investors had largely made up their minds.
"The markets have voted, and it's 'remain,'" said Quincy Krosby, market strategist at Prudential Financial in Newark, New Jersey. "What you see is basically an unwinding taking place in terms of the dollar weakening, British pound sterling ... moving decisively higher, and not surprisingly, the commodity currencies have been moving higher as well."
An Ipsos MORI poll for the Evening Standard on Tuesday and Wednesday showed 52 percent of British voters would opt to remain, while 48 percent would vote to leave. An online Populus poll showed 55 percent support for staying in the EU.
Earlier polls by ComRes and by YouGov also showed a last-minute rise in support for remaining.
Sterling rose to $1.4946, its highest against the dollar since Dec. 31, in early trading. The pound was last up 0.8 percent at $1.4830.
The euro touched a six-week high of $1.1421 against the dollar, also on the back of increased odds that Britain will remain in the 28-member European bloc. The currency was last up 0.8 percent at $1.1385.
Both the euro and pound also rose against the safe-haven yen, which took a beating as traders favored riskier assets. The euro gained more than 2 percent against the Japanese currency, moving to 120.88 yen. Sterling added more than 2.5 percent to 158.05 yen.
The dollar also gained against the yen, rising to 106.03 yen, its highest level in more than a week. It was last up 1.3 percent at 105.72 yen.
Voting in the British referendum will end at 2100 GMT (2200 BST), with results expected early on Friday.
Commodity-linked currencies surged, with the New Zealand dollar rising to its highest against its U.S. counterpart since May 2015.
Emerging market currencies got in on the rally as well, with the Mexican and Colombian pesos and the South African rand rising by more than 1 percent against the greenback.