Brexit uncertainty, Thomas Cook has said.
The travel firm says almost half (48%) of the holidays it sold up until the end of February were to non-EU destinations, up 10% on last year.
Despite this, the firm says Spain is still its most popular destination.
Its findings chime with separate Post Office figures showing currency sales for long-haul destinations have jumped.
Sales of the Japanese yen were up 12% so far this year compared with last, while sales of the Indonesian rupiah have increased by 9%, Post Office Travel Money said.
The figures are based on Post Office transactions between 1 January and 23 April. The Post Office accounts for about a quarter of all UK currency transactions.
It said the biggest growth in currency sales so far this year has been for the Egyptian pound, which has seen a 687% year-on-year increase.
Thomas Cook - through which 19 million people book holidays each year - said after Spain, Turkey had proved the most popular destination for its holidaymakers, accounting for a quarter of its flight-only bookings so far.
Thomas Cook said Tunisia was also "faring well" with package bookings to the country double that of last year, with flight-only bookings up four-fold.
Tourism to the country fell dramatically after a 2015 terrorism attack in the resort of Sousse in which 30 British tourists and eight others were killed by a gunman with links to Islamic State.
The Foreign and Commonwealth Office lifted its travel ban against the country last year, prompting British operators to renew flights to Tunisia's Mediterranean coast.
Thomas Cook has made two profit warnings in the past six months following drops in holiday bookings. In March, it detailed plans to close 21 stores across the country and cut more than 300 jobs.
Chief executive Peter Fankhauser said it was still too early to tell the impact on bookings of the UK's exit from the European Union being delayed to the end of October.
But he said there was "little doubt that the prolonged uncertainty around the manner and timing of Britain's exit from the European Union has led many customers to press pause on their holiday plans for this summer".
Please include a contact number if you are willing to speak to a BBC journalist. You can also contact us in the following ways: