Nearly 1,000 holidaymakers on Thomas Cook packages in Gambia are to be flown home amid growing concerns of political unrest in the west African nation.
The holiday company said it had triggered contingency its plans after the Foreign Office (FCO) urged Britons to avoid all non-essential travel to the winter destination.
A 90-day state of emergency has been declared in the country where political deadlock has led to a "high" risk of military intervention and civil disturbance, the FCO said.
The Association of British Travel Agents (Abta) estimates there are around 2,000 people are currently on holiday with its members in Gambia, while an additional number will have travelled there independently.
Abta advised British tourists on package holidays to contact their tour operator to arrange return flights, while anyone who has travelled independently should speak to their airline.
It is understood that at least one flight carrying British holidaymakers flew to Gambia as recently as Tuesday morning.
Thomas Cook said a flight scheduled from Manchester to Gambia on Wednesday will now depart without customers and bring the first groups of holidaymakers home.
An additional four flights have been arranged from the capital Banjul back to the UK on Wednesday, with two scheduled to fly to Manchester and two to Gatwick.
A spokesman said: "We will operate a programme of additional flights into Banjul airport over the next 48 hours to bring the 985 UK customers we currently have on holiday in the Gambia home, including four additional flights on Wednesday 18 January.
"In addition, we have approximately 2,500 flight-only customers in Gambia, whom we are contacting to offer the earliest possible flight availability for return to the UK."
The company said staff will be flying to the country to assist on Wednesday.
Gambia's popularity as a winter sun destination has grown in recent years, with holidaymakers drawn to its white sandy beaches and tropical climate by affordable deals.
However the country was thrown into political crisis in December after president Yahya Jammeh refused to accept electoral defeat.
The country's president-elect, Adama Barrow, left the country as the incumbent leader challenged the result in the courts.
The FCO said it had received reports that the sitting government had closed down opposition radio stations and made politically motivated arrests.
Meanwhile the Economic Community of West African States has stated it may intervene, including taking possible military action, if Mr Jammeh does not step down by the scheduled handover date of January 18/19.
On Tuesday the FCO advised against all non-essential travel to country and urged Britons in Gambia to be vigilant and keep in contact with their holiday company.
A spokesman said: "The potential for military intervention and civil disturbance is high and could result in Banjul International Airport being closed at short notice.
"You should follow events closely, take extra care, keep in regular contact with your tour operator and airline and continue to monitor travel advice and social media updates in case tensions rise as the current political deadlock continues."
Abta said anyone with a holiday to Gambia booked should contact their travel company to discuss their options.
A spokesman said: "The political situation remains fluid and the FCO travel advice will reflect this. Travel companies will continue to monitor the situation and allow cancellations and rebooking for travel dates while the advice against all but essential travel remains in place."
Thomas Cook said anyone due to travel to Gambia with them should call 01733 224 536.