The Foreign Office urged UK tourists to leave immediately and warned against all but essential travel to the country following intelligence a terrorist attack is “highly likely”.
It comes a fortnight after 30 Britons were among 38 tourists killed on the beach in Sousse by gunman Seifeddine Rezgui. Terror group Islamic State claimed responsibility for the attack.
The new advice is another hammer blow for the Tunisian tourist industry and has sparked fears it could play into the hands of extremists in the North African country.
Nabil Ammar, Tunisian ambassador to the UK, told BBC Two’s Newsnight: “This is what the terrorists want.
“By damaging the tourism, by having foreigners leaving the country, they damage the whole sector and put so many people out of work and on the streets.
“Hotels have to close and this is an important industry.
“One of the sources of terrorism is lack of hope. It is not the only motor of it but it is one of the very important origins.”
Extra flights have been laid on to evacuate up to 3,000 British package holidaymakers and 300 independent travellers believed to be in Tunisia.
Tourists will begin to be flown out of the country this morning.
The Sousse beach massacre came just months after 22 people, mostly tourists, were killed at the National Bardo Museum outside Tunis in March.
Foreign Secretary Philip Hammond said: “Since the attack in Sousse the intelligence and threat picture has developed considerably, leading us to the view that a further terrorist attack is highly likely.”
Following the Government’s warning, Thomson and First Choice immediately cancelled all flights to Tunisia for the summer season.
They added that “as a precautionary measure we have taken the decision to repatriate all British Thomson and First Choice staff currently working in Tunisia within the next 24 hours”.
Thomas Cook, which cancelled all future bookings to Tunisia up to October 31, said it is putting on an extra flight today to bring its customers back to the UK.
The returning holidaymakers will touch down in Manchester as some of the funerals of the Britons killed in Sousse take place.
Family and friends of Jim and Ann McQuire, of Cumbernauld, North Lanarkshire, will say their final farewells at a service at Abronhill church in their home town this afternoon.
Tunisia has announced plans to build a barrier along the border with Libya - including fencing, a sand wall, trenches and surveillance posts - to keep out extremists following recent terror attacks.
Holidaymakers should contact their tour operators about returning to Britain and independent travellers should make their own arrangements to leave, the Foreign Office said.
A Thomas Cook spokesman said: “The safety and well-being of our customers is our primary concern.
“In response to the recent change in FCO (Foreign and Commonwealth Office) advice we have taken this decision to bring all Thomas Cook customers back to the UK as soon as we can using third party carriers and on our ten scheduled flights over the weekend.
“Thomas Cook is strongly advising its guests in the country to return on these flights. We are also sending our specialist assistance teams to Tunisia to offer customers additional support in resort.”
Monarch Airlines said it is arranging to repatriate all customers in resorts “back to the UK as soon as possible”. Flights have been organised to take them out of Tunisia by this weekend.
The airline is cancelling all flights to Enfidha in Tunisia for the rest of the summer season with “immediate effect”.
All customers who have already booked to travel there will get a full refund or credit or they may be able to change their destination.