The British Foreign & Commonwealth Office has changed its level of advice to The Gambia and now advises against “all but essential” travel to the country.
The decision comes as Gambian president Yahya Jammeh declared a 90-day state of emergency a day before his official mandate ends.
Citing “extraordinary” foreign interference in his Gambian affairs, he has clung to power since being defeated in an election in December.
Regional leaders have been unsuccessfully trying to persuade Jammeh to hand over power to Adama Barrow, who won the polls.
ABTA estimates there are around 2,000 people currently on holiday with its members in The Gambia.
Many of these are now expected to fly home at the political situation in the country deteriorates.
There are also an unknown number of people who have travelled independently either for a holiday or to visit friends and family.
Package holidaymakers in The Gambia are advised to contact their tour operator to confirm arrangements for returning home.
Those who have travelled independently will need to contact their airline to discuss their options.
Tour operators will not send out any further package holidaymakers to the Gambia while the FCO advice remains in place.
Thomas Cook has said it will fly 1,000 travellers home.
Independent travellers should be aware that travelling to The Gambia at this time will invalidate their UK travel insurance policies.
Insurance policies will still provide cover for travellers already in a country at the time of a Foreign Office advice change.
Package holidaymakers due to travel imminently to The Gambia are advised to contact their tour operator to discuss the options of changing their date of travel, receiving a full refund or booking an alternative holiday.
Independent travellers should talk to their airlines and accommodation providers, although there is no obligation on either to offer the same options as a tour operator.
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.
In a statement Adboulie Hydara, director general, Gambia Tourism Board, added: “We are monitoring the political situation and are working closely with our UK tour operator partners to support them in returning customers to the UK.
“All holidaymakers with independent flight bookings are advised to contact their flight provider to discuss travel options.
“For those with future bookings to the Gambia we advise that they speak to their holiday provider to change their date of travel.
“We will continue to monitor the situation carefully and share updated advice accordingly.
“As a popular winter sun destination among British holidaymakers, the safety of our visitors is of the upmost importance and we look forward to continuing to welcome them once the situation has been fully resolved.”
Although modest in total numbers, in recent years The Gambia has become an increasingly popular winter sun destination.