Holidaymakers have been scrabbling to buy up foreign currency over fears the pound could fall further after Britain voted to leave the European Union.
Thomas Cook announced that it was suspending all online currency sales due to "unprecedented demand" on Friday afternoon and also restricted online orders to be picked up in store that were made yesterday to £1,000.
There were long queues outside some branches as the chain tried to avoid its counters running out of money, according to the BBC.
A spokesperson said: "We have temporarily suspended our travel money website following unprecedented customer demand for foreign currency overnight and this morning.
"We apologise to all customers affected. Our immediate priority is to ensure that we have enough currency in store to fulfil outstanding orders. We hope to be back up and running as soon as possible."
The BBC reported that the euro was in high demand, with the pound down more than 5% against it at €1.2398 in Friday trading.
Meanwhile the it fell 10% against the dollar overnight to $1.33 - a 30-year low.
Writing on MoneySavingExpert.com, Martin Lewis said that it was difficult to know when the best time to buy currency would be.
He said: "I'm afraid I can't answer that without a crystal ball. There is huge volatility on the currency markets and they could move any way.
"If you're worried, one option is to buy from a firm that allows you to order but with a cancellation right. So you lock in today's rate, but if it improves you cancel and buy elsewhere (see my blog on Buying euros/dollars before the referendum, which still relevant now as it's about protecting yourself from volatility).
"Or you could go for a top overseas spending card that gives you perfect exchange rates on the day you spend."
Some British tourists in Europe were already reporting issues trying to exchange British currency:
Last month David Cameron claimed that Brexit would cause a family holiday to cost £230 more - it now remains to be seen if this is true.
Europe is also the most popular holiday destination for Brits, with some 47 million visits in 2014, according to the BBC.
Andrew Shelton, Managing Director of global flight search and travel deals website, Cheapflights.co.uk, also pointed out that EU agreements that which helped to facilitate cheap travel had been taken for granted.
He said: "Today’s referendum result will throw the spotlight onto many benefits British travellers have taken for granted for years, including the agreements which created the environment for the budget airlines to thrive and kept airfares low across the board and encouraged the free movement of people, a currency deal that has made the Eurozone so cheap to visit for years, the end of mobile data roaming charges, and free healthcare within the EU."
Shelton did add though that the decision to leave the EU was not necessarily a huge problem.
He said: "Holidaymakers shouldn’t assume that Brexit means all that will be lost. The UK travel market is vital to the economy of many European countries and regions. It will be in their interests to seek ways to maintain the status quo.
"The Government must now work hard to secure deals with the EU that support our vibrant industry and we believe maximum effort will be going in from all sides in the coming months and years to ensure the UK cash cow isn’t put out to pasture."
The dramatic result wiped £122 billion of the value of the FTSE 100 within minutes - it dropped to 5,788.74 just after opening, a dramatic fall of more than 8%.
The pound has plummeted to a low not seen since 1985.
According to sources including the London Economic digital newspaper, the drop may mean the UK is no longer the fifth biggest economy in the world and France has “overtaken us”.