Yahya Jammeh, an authoritarian president who ruled for 22 years, has confirmed he will step down.

"I will help him work towards the transition," Mr Jammeh said on state TV on Friday evening, after speaking to the president-elect by telephone.

Mr Barrow, 51, who has never held political office, won Thursday's election with 45.5% of the vote.

Hundreds of Gambians took to the streets to celebrate one of the biggest election upsets West Africa has ever seen.

Mr Jammeh, also 51, took power in a bloodless coup in 1994 and has ruled the country with an iron fist ever since.

President Jammeh took 36.7% of the vote, while a third party candidate, Mama Kandeh, won just 17.8%.

The BBC's Umaru Fofana, who spoke to Mr Barrow, said the president-elect seemed bewildered by the result.

President Jammeh has congratulated the property developer and vowed not to contest the results after deciding "that I should take the backseat".

Who is Adama Barrow?

"I am very, very, very happy. I'm excited that we win (sic) this election and from now hope starts," Mr Barrow told the BBC's Umaru Fofana, adding that he was disappointed not to have won by a larger margin.

Born in 1965 near the eastern market town of Basse, Mr Barrow moved to London in the 2000s where he reportedly used to work as a security guard at an Argos catalogue store.

He returned to The Gambia in 2006 to set up his own property company, which he still runs today.

Mr Barrow, who is leading an opposition coalition of seven parties, has promised to revive the country's struggling economy, look at imposing a two-term presidential limit and introduce a three-year transitional government.

Why was it such a shock? By Alastair Leithead, BBC Africa correspondent

Despite a surge of support for an opposition broadly united behind one candidate, most people expected the status quo to prevail.

Hopes weren't high for a peaceful transfer of power, with a crackdown on opposition leaders months before the polls, the banning of international observers or post-election demonstrations, and then the switching off of the internet on election day.

But in a place where glass beads are used in place of ballot papers, it seems that the marbles have spoken.

The unseating of an incumbent president is not the usual way politics goes in this part of the world - but it's becoming popular in West Africa at least, with Muhammadu Buhari unseating Goodluck Jonathan in Nigeria just last year.

Former businessman Adama Barrow now has his chance to tackle the poverty and unemployment which drives so many young Gambians to join the Mediterranean migrant trail every year.

How has incumbent President Jammeh reacted?

The incumbent president has asked his successor to set up a time to meet and organise the transition period.

Yahya Jammeh, a devout Muslim, had once said he would rule for "one billion years" if "Allah willed it".

"It's really unique that someone who has been ruling this country for so long has accepted defeat," the electoral commission chief, Alieu Momar Njie, said on Friday.

Human rights groups have accused Mr Jammeh, who in the past claimed he could cure Aids and infertility, of repression and abuses of the media, the opposition and gay people.

In 2014, he called homosexuals "vermin" and said the government would deal with them as it would malaria-carrying mosquitoes.

Several previous opposition leaders were imprisoned after taking part in a rare protest in April.

Mr Barrow has promised to undo some of Mr Jammeh's more controversial moves, including reversing decisions to remove The Gambia from the Commonwealth and the International Criminal Court (ICC).

Where is The Gambia?

The Gambia is the smallest country on mainland Africa, with a population of fewer than two million.

It is surrounded on three sides by Senegal and has a short Atlantic coastline popular with European tourists.

Tourism has become The Gambia's fastest growing sector of the economy, and it is known to travellers as "the smiling coast of West Africa".

Last year, President Jammeh declared the country an Islamic Republic in what he called a break from the country's colonial past.