The UK formally left the European Union on Friday, giving up its membership of 47 years, in a move that could trigger seismic political and economic ramifications for the EU and the continent itself.

In a statement that appeared to be infused with optimism, Prime Minister Boris Johnson said: "Tonight we are leaving the European Union. For many people this is an astonishing moment of hope, a moment they thought would never come. And there are many of course who feel a sense of anxiety and loss. And then of course there is a third group – perhaps the biggest – who had started to worry that the whole political wrangle would never come to an end.

"I understand all those feelings, and our job as the government – my job – is to bring this country together now and take us forward. And the most important thing to say tonight is that this is not an end but a beginning. This is the moment when the dawn breaks and the curtain goes up on a new act in our great national drama."

Britain's departure from the bloc, which took place at midnight CET, brings to a close three-and-a-half years of a bitter political tug-of-war. It has led to division within the UK and acrimony with Brussels after Britons opted for a future outside the EU in a nationwide referendum in June 2016, albeit with a slim majority.

Celebrations erupted across the country to mark the historic event. Singing patriotic songs and waving Union Jack flags, thousands of people gathered outside the parliament in central London.

Tony Williams, 53, from south-east London said: "This is a fantastic day, a really, really fantastic day. It's been a long time coming.

"We are free, from 11 o'clock, we have done it, and it is a great, great pleasure. We have done it."

Protests were held as well by the Remain camp in different parts of the UK. Some pro-Europeans, including EU citizens who have made Britain their home, marked the occasion with solemn candlelit vigils. 

The mood in Europe was equally somber.

French President Emmanuel Macron said: "This is a sad day, there's no hiding it. But it's also a day which should prompt us to proceed in a different way.

"To build with more determination a European Union that is powerful, effective, which you find more convincing and which rediscovers the historical path that makes this European Union a unique and, in my eyes, irreplaceable adventure."

EU chief negotiator Michel Barnier told the BBC: "Today my thoughts go to the millions of British citizens who are sad, as we are sad today."

Britain will now enter a transition period for the next 11 months with London and Brussels presiding over an extremely complicated decoupling process. Formal negotiations will begin on 3 March.

Buoyed by the decisive electoral victory in December 2019, Johnson and his Conservative Party are confident of drawing up robust and forward-looking ties with the EU, its largest trading partner.

Brussels, however, has warned that the British government's negotiating timeline was highly ambitious, raising fears of a "hard Brexit" at the end of 2020.

It's just not the EU, the UK is staring at a foreign policy conundrum as it strives to thrash out trade deals with the rest of the world, an exercise that would throw up myriad challenges and stretch government resources to the limit.

Brexit has provoked soul-searching in Brussels, too. European Commission President Ursula von der Leyen said that Britain leaving the EU was proof that the bloc must deliver results for its people.

She told broadcaster ARD: "We must stand up for Europe, otherwise at some point we won't have it any more.

"Europe must deliver on the biggest questions - that's what we need the European level for."