With only a few weeks to go until Britain holds its referendum, fresh polls have shown an increase in support among voters for the U.K. to leave the European Union, swinging toward a Brexit.

The polls come as campaigners step up their push to influence voters ahead of the in/out referendum on June 23, which will decide whether the U.K. should withdraw from membership of the bloc.

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Results from a online poll released Monday by ICM showed those wishing to leave the EU at 48%, and those wanting to remain in at 43%. Factoring in the 9% “don’t know” responses, that equates to 53% in favor of a Brexit and 47% opposed, the research firm said.

“After a fairly tumultuous week in which both Prime Minister [David Cameron] and Michael Gove set out their stalls on TV, ICM’s weekly tracker and indeed at least two other polls published in the last 24 hours suggest a move to Leave might have occurred,” ICM’s Martin Boon said in a post online.

A separate YouGov poll for ITV’s “Good Morning Britain” television show put those wishing the U.K. to leave the EU at 45% and those wanting to remain at 41%, while 11% said they were undecided. That research covered 3,495 people and was carried out online from June 1 to 3.

Those shifts were reflected in two other opinion polls. An Opinium survey found a three-point lead for “leave” in a poll for the Observer newspaper published at the weekend. And research firm TNS found those in favor of a Brexit at 43%, versus 41% who want to reject it, according to Reuters. TNS polled 1,213 Britons between May 19 to 23.

The polls took a bite out of the British pound GBPUSD, +0.02% , which dropped on Monday to a three-week low of $1.4353. The pound recently traded down 0.3% on the day, at $1.4471.

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The results reflect a shift in public opinion shown last week in a Guardian/ICM poll, which reported 52%-48% split in favor of a Brexit. Earlier, polls were showing a lead for the “remain” camp, and that first sign of a swing was followed by sharp losses for the British pound.

But “polls in the final weeks tend to overstate the support for change,” Citigroup noted last week, citing research from Elections Etc. that looked at previous referendums. The polls contract the odds offered by bookmakers on the results of the poll, which indicate strong support for a “stay” vote.

Read:Bookies still deem Brexit unlikely — and for good reason, Citi says

“While I would expect more downside if the polls continue to show the ‘Leave’ campaign gathering momentum, the pound is likely to be very volatile in both directions over the next couple of weeks,” said Craig Erlam, senior market analyst at Oanda, in a note.

“The polls are having a significant impact on the pound, and some of them are sending very different messages,” he added.

ICM sounded a note of caution, pointing out that opinion research conducted by telephone have not generally shown the same mood as online responses.

“All these polls were conducted online, however, and outside of ICM’s unexpected leap toward Leave in our phone poll last week, no other evidence has been forthcoming from phone polls that Remain are falling back,” Boon wrote.

“If new phone polls do emerge with such an outcome, however, we could be more confident that — irrespective of where the actual standings are on a poll-by-poll basis — Leave have pushed on.”

The Organization for Economic Cooperation and Development warned last week that the possibility of Brexit would have major downside risk for not only the U.K., but the rest of the world.