If the UK voted to exit the European Union (EU), currency traders would likely dump the pound and send funds into the dollar, FX pros said.

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The Brexit referendum, which will decide whether the UK remains in the 28-member trade block, was set to begin Thursday, with results due early Friday local time. Broadly, opinion polls showed the remain and leave camps were neck-and-neck, making the result too close to call.

If there was a Brexit, analysts broadly expected a surge in market volatility amid uncertainty over what would happen next.

"The idea that having taken a vote to leave the EU and then say, 'This is what Britain will now look like, this is how it will now be,' is not based on any form of reality, because you don't know what that treaty process will look like," Mark Todd, director of fixed income for NAB, told CNBC's "Squawk Box."

"You don't know what the reaction in Europe will be towards you as treaty partner, you don't know what demands they will make and you certainly don't know what will happen to asset prices."

Todd expected a Brexit would push markets into risk-off mode in a "fairly significant manner," sending investors into cash.

But with cash rates negative in much of the world, he expected most to opt for the greenback, with potential negative implications for the US economy.

Other analysts expected a Brexit would send further flows out of sterling.

The pound has tumbled this year, falling as low as USD 1.4089 in June before recovering to as high as USD 1.4842 during the Wednesday US session, its high so far this year, after recent opinion polls started to indicate the remain camp held a tenuous lead.

"A leave vote would come as something of a shock," given the market appeared to be leaning toward pricing in a remain vote, Sarah Hewin, head of research for Europe at Standard Chartered, told CNBC's "Rundown."

Her bank's forecast was for the pound to drop to the low USD 1.20s if the leave camp won, but rise to the USD 1.50s on a remain vote.

But she added, "We would expect, whatever the outcome is going to be, a lot of volatility over the next 24 hours. "