Tens of thousands of residents have fled, as troops from Nigeria and Senegal prepare to invade the country and use force to install Mr Barrow as the rightful president on January 19.
Mr Jammeh initially accepted the December 1 election result, but a week later, he reversed his decision, claiming that voter fraud had cost him the election. He has since petitioned Gambia’s Supreme Court for a re-run of the polls, in what critics have said is simply an attempt to cling to power. On Wednesday Gambia’s parliament voted to extend his term by 90 days.
Delegations led by the Economic Community of West African States (ECOWAS) and its president Ellen Johnson Sirleaf have tried to convince Mr Jammeh to step aside, to little result.
The West African bloc is now preparing to use force to end Mr Jammeh’s rule and install Mr Barrow in the presidential office.
The Nigerian government last week authorised generals to mobilise an 800-strong battalion to spearhead the mission and on Wednesday confirmed that a warship was heading toward Gambia for “training” as regional countries prepared to intervene. Columns of Senegalese troops also moved to the Gambian border on Wednesday.
Mr Barrow has been in neighbouring Senegal since last week, amid fears that he could be thrown in jail or even killed if he stayed in Gambia ahead of taking charge.
He is due to hold his inauguration at the Banjul’s Independence Stadium on Thursday, but to avoid trouble, diplomats say he could end up being sworn in at the Gambian embassy in Senegal.
Britain’s Foreign Office has warned of a “high” potential for unrest in the country, which, despite Mr Jammeh’s fearsome reputation, has become a popular winter holiday destination in recent years.
More than 1,000 mainly British and Dutch tourists began leaving the tiny West African nation on specially chartered flights on Wednesday. Hundreds streamed into the airport, seeking information on departures.
At least 26,000 citizens had fled Gambia into Senegal by Wednesday afternoon.
Where is Gambia?
Gambia is the smallest nation in mainland Africa, with a population of just 1.9 million people – including an army of just 900 soldiers. It follows the shape of the Gambia river and is surrounded on three sides by Senegal.
The former British colony gained independence from Britain in 1965 and has had just two leaders since.
Who is Yahya Jammeh?
Mr Jammeh, who styled himself “Excellency Sheikh Professor Doctor President”, had been in office since a coup 22 years ago, ruling through a cult of fear that fused witchcraft with oppression.
He claimed to have invented his own herbal cure for HIV, and once “exorcised” an entire village of 1,000 people by force-feeding them hallucinogenic potions.
A self-declared “dictator of development and progress,” he did enjoy some popular support, mainly for developing Gambia’s infrastructure and beach tourism trade, which attracts 50,000 Britons a year.
But he was also criticised for jailing and torturing thousands of critics, some of whom did not leave prison alive.
In 2013, Mr Jammeh pulled Gambia out of the Commonwealth in 2013, saying it was a “neo-colonial institution”.
Last year, he also withdrew Gambia from the International Criminal Court, describing it as the “International Caucasian Court”.
The former army officer appeared to be turning over a new leaf, conceding defeat to opposition candidate Adama Barrow, but a week later, he reversed his decision, claiming that voter fraud had cost him the election.
Who is Adama Barrow?
Adama Barrow, 51, is the president-elect of Gambia, who is expected to be inaugurated on Thursday, January 19.
On December 1 2016, Mr Barrow staged a shock victory over incumbent president Yahya Jammeh.
While elections in the small West African nation would not normally draw a lot of international media attention, Mr Barrow’s links to the United Kingdom and unexpected win have pushed his story up the agenda.
Mr Barrow, who is married with two wives and four children, lived in London between 1998 and 2002, studying property management and working in a variety of security jobs.
He spent some time as an Argos catalogue store security guard, tackling shoplifters on London’s Holloway Road. One of thief he caught was later jailed for six months.
Mr Barrow said during the election campaign that his time in Britain helped his political career by teaching him the importance of time-keeping and working long hours.
He has promised to reverse many of the controversial measures taken by his predecessor, who tried to take Gambia down a radically anti-Western path.
Mr Barrow had a fifth child, an eight year old son called Habibu, who died after being bitten by a dog on Monday.
What is ECOWAS and who is invading Gambia?
ECOWAS is the acronym for the Economic Community of West African States, the economic bloc made up of 15 member countries. Those countries are: Benin, Burkina Faso, Cape Verde, Ivory Coast, Gambia, Ghana, Guinea, Guinea Bissau, Liberia, Mali, Niger, Nigeria, Senegal, Sierra Leone and Togo.
Ellen Johnson Sirleaf, the president of Liberia, is the head of ECOWAS and has been heavily involved in negotiations with Mr Jammeh.
Military intervention in Gambia will mostly involve troops from neighbouring Senegal and Nigeria, which has the greatest military might of the region.
How are Foreigners affected
An estimated 100,000 tourists visit Gambia every year, roughly half of them Britons. The rest are largely from the Netherlands. Some 5,000 Britons now live there permanently.
On Wednesday, nearly 1,000 British tourists are due to be flown back from Gambia by holiday company Thomas Cook after the Foreign Office changed its travel advice because of political unrest in the West African country.
In the Netherlands, travel company Corendon said it was sending planes to Gambia to bring home tourists. The company said 831 Dutch tourists were on Corendon vacations there.
Another Dutch tour operator, Tui, was sending five aircraft to repatriate Dutch and Belgian tourists. Tui said it had 815 Dutch tourists and 228 Belgians in the country.