The "too-close-to-call" and "knife-edge" prediction of the opinion polls seem to hold true as Remain were at 50.7 per cent and Leave at 49.3 per cent with 146 out of 382 results declared.
More than 6 million voters have voted for Remain, while 5.8 million have voted for Brexit so far. The broad trends indicate that the side in favour of Brexit, or Britain's exit from the EU, was showing a stronger than expected performance than initially expected.
"At this very early stage, the Leave side has done much better and even looks like the favourite to win the referendum," BBC polling expert Prof John Curtice said.
Northeast England and Wales seem to be backing Brexit, while Scotland and Northern Ireland appear to have opted for Remain - but millions of votes still remain to be counted in the referendum, which has registered a 70 per cent turnout - higher than the 2015 General Election.
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Unlike at a General Election the results in individual areas do not count as it is the overall number of votes cast for one side or the other across the country that will determine the outcome.
The side which wins more than 50 per cent of the votes at the end of the count would be considered to have won.
The final national result is to be officially declared by the UK Electoral Commission's chief counting officer, Jenny Watson, from Manchester Town Hall.
Brisk voting marked polling day yesterday as the results remained too close to call till the very last minute.
Experts had predicted that a high turnout would benefit the Remain campaign. The final announcement will bring to a close a fever-pitched and highly-strung campaign by both the Brexit and Remain sides.
There has been much speculation about how the final outcome would impact David Cameron's own political future as Prime Minister. While he has repeatedly stressed that the 2015 General Election has given him the mandate to continue irrespective of the result, the bitter campaign had exposed a deep divide within his own Conservative party.