British tour operators Thomson and First Choice sent 10 planes to evacuate tourists from Tunisia on Saturday after 39 people including at least 15 Britons were killed in the resort of Sousse in an attack claimed by Islamic State.
The British government said it expected the number of British casualties to rise after the attack on Friday at the Imperial Marhaba hotel in Sousse, 140 km (90 miles) south of the capital Tunis. Other casualties included German and Belgian tourists.
"I expect it (the number of British casualties) to increase," British Defense Secretary, Michael Fallon, told the BBC. "Most of the people were British and there were a large number of British caught up in the shooting."
A gunman disguised as a tourist opened fire on tourists as they lounged on the beach at the hotel, with a rifle he had hidden in an umbrella.
Thomson and First Choice said several of the people killed and injured were their customers and that they were working closely with the local authorities to confirm the exact details of casualties.
The tour operators said 10 Thomson Airways flights had gone to Tunisia to repatriate all of the companies' customers from Port El Kantaoui and Sousse, a total of approximately 2,500 people.
British Prime Minister David Cameron was due to chair a meeting of senior ministers on Saturday to discuss the response to the attack in Tunisia.
"I'll be chairing a COBRA meeting of senior ministers and officials shortly to continue discussing our response to the Tunisia terror attack," Cameron said on his Twitter account, referring to a meeting room where high-level security meetings take place.
The Foreign Office confirmed late on Friday that five Britons were among the dead but the British death toll was expected to rise. Tunisia is a popular holiday destination for British tourists.
The tour operators said they would be cancelling all Thomson and First Choice holidays to Tunisia for the next week, and that amendments could be made to bookings on holidays to Tunisia until July 24 with extra flights to Cape
Verde, Rhodes and Gran Canaria offered as alternatives.