The first results in the UK’s referendum on whether to remain in the European Union are coming in.
After results in 15 counting areas out of 382, Remain was on 48.5% and Leave on 51.5%, with Leave doing well in the North-East of England and Remain ahead in Scotland.
A full picture is not expected for some hours but turnout looks set to be higher than for the general election.
The pound surged as polls closed before falling dramatically.
Unlike at a general election the results in individual areas do not count – it is the overall number of votes cast for one side or the other across the country that will determine the outcome.
Polling expert Prof John Curtice said at this very early stage Leave looked favourite to win the referendum. He estimates that the finishing post for one side to win is 16,813,000 votes.
The pound surged against the dollar when polls closed at 22:00 BST and opinion polls pointed towards a Remain win but it fell dramatically when the first results were declared.
Votes are being counted at each of the 382 local counting areas. These represent all 380 local government areas in England, Scotland and Wales, plus one each for Northern Ireland and Gibraltar.
Results from these areas will then be declared throughout the night, along with result totals from 11 nations and regions.
Jenny Watson, chief counting officer, will announce the referendum result at Manchester Town Hall after all 382 local totals have been certified and declared.
Gibraltar was the first to declare a result with 96% of voters in the British overseas territory backing Remain. A big Remain win had been predicted in Gibraltar amid concerns about its border with Spain.
Leave won by 22% in Sunderland, but Remain edged it in neighbouring Newcastle but by a tighter margin than expected, in two of the first results to declare.
According to Prof Curtice, the Remain vote is about 10% short of what was expected in the North-East of England and although Remain is ahead in Scotland, turnout is lower than in the rest of the UK.
Wales appears to be leaning towards Brexit, with a vote of 54.9% for Leave after four voting areas had declared.
Northern Ireland, with five constituencies declared so far, is voting in favour of Remain.
There are no results so far from the Midlands, Yorkshire and Humber or London and South East of England, where voting was disrupted by flash flooding.
An online survey taken on polling day of 5,000 people by YouGov suggests the Remain side running at 52% of the vote, to Leave’s 48%. Ipsos Mori have released polling from Thursday and Wednesday suggesting Remain will get 54% and Leave 46%.
UK Independence Party leader Nigel Farage told the Press Association the Remain camp had won based on “what I know from some of my friends in the financial markets who have done some big polling”.
In a speech to supporters in London, Mr Farage – whose political career has been built on campaigning to get the UK out of the EU – said his “sense” was that the UK had voted to Remain.
He told the cheering crowd he hoped he was wrong but added: “Win or lose this battle, we will win this war, we will get this country back.”
Analysis by BBC Political Editor Laura Kuenssberg
Several months ago, the Leave campaign didn’t have much hope that they could get anywhere close in a short campaign.
They characterised themselves as the plucky underdogs, in with a shout, but certainly the real outsiders.
But, in part by using that status, indeed building a narrative of the people versus the elites, they have got themselves to a position where they might end up on the winning side.
The referendum result, which should be known by breakfast time on Friday, could be a turning point in the UK’s relationship with Europe and the rest of the world.
If the UK becomes the first country to exit the EU it will arguably be the biggest blow to the 28-nation European Union since its formation.
A vote to remain would see Britain gain exemption from “ever closer” political union and other concessions secured by Prime Minister David Cameron in a renegotiation of the country’s membership terms.