London: Britain has officially left the European Union (EU), marking a historic end to its 47-year-long membership of the world's largest trading bloc.

The historic moment happened at the stroke of 23:00 GMT on Friday, more than three and half years after an in and out referendum exposed deep rifts across British society.

It also marks the start of a transition period that will last till the end of this year as negotiators try to forge a trade arrangement between Britain and the EU, Xinhua news agency reported.

While celebrations to mark "Brexit day" saw EU flags being burned on the streets of London, UK Prime Minister Boris Johnson marked the historic moment with his team at his Downing Street office, celebrating with English sparkling wine and an array of British culinary treats, Aljazeera reported.

As the clock ticked down the final seconds, thousands of Brexiters partied outside Parliament, while anti-Brexit campaigners mounted several protests along the Irish border.

In a televised address to the nation, Johnson called the UK's withdrawal from the EU "an astonishing moment of hope" .

"This is the moment when the dawn breaks and the curtain goes up on a new act in our great national drama," he said.

"And yes it is partly about using these new powers - this recaptured sovereignty - to deliver the changes people voted for. Whether that is by controlling immigration or creating freeports or liberating our fishing industry or doing free trade deals. Or simply making our laws and rules for the benefit of the people of this country.

"And of course, I think that is the right and healthy and democratic thing to do," he added. "Because for all its strengths and for all its admirable qualities, the EU has evolved over 50 years in a direction that no longer suits this country."

The Prime Minister called for "a new era of friendly cooperation between the EU and an energetic Britain".

In Scotland, which voted to stay in the EU in the 2016 referendum, rallies and candlelit vigils took place as activists sought to send a message to the EU to keep open a place for Scotland.

In Northern Ireland, the campaign group Border Communities Against Brexit staged a series of protests in Armagh, near to the border with the Republic of Ireland.

In Cardiff, First Minister Mark Drakeford said Wales would "remain a proudly European nation".

Meanwhile leaders across Europe gave their reactions to the first country leaving the EU.

German Chancellor Angela Merkel said Brexit was "a deep break for us all" and warned the "negotiations will certainly not be easy".

French President Emmanuel Macron said Brexit was an "alarm signal" for the EU and hit out at the "lies, exaggerations, simplifications" that led to the Leave vote.

The departure, 1,317 days after Britain voted to leave the bloc, carries not only enormous symbolic weight, but also significant legal consequences.

It concluded three years of fractious debates over whether the country should really leave the bloc, the terms of its departure and the kind of relationship it should forge with Europe.