The United Kingdom officially left the European Union on Friday, making the country the first to leave the 28-member bloc since 1973. 

In the biggest shift since losing its global empire, the United Kingdom slipped away at 2300 GMT, turning its back after 47 years on the post-World War Two project that sought to build the ruined nations of Europe into a global power.

While the UK has agreed to the terms of its EU departure, both sides still need to decide what their future relationship will look like.

Read more: Johnson: This is not an end but a beginning

Brexit: What changes for the UK and the EU from 1 February?

At the EU headquarters in Brussels, the British flag was lowered. Little will change immediately, however, as a transition period keeps the United Kingdom as a member in all but name until the end of 2020.

On June 23, 2016, about 17.4 million Britons voted in favor of Brexit, triggering political and market turmoil in the UK. 

Cheers and tears

Beside the British parliament, flag-waving Brexit supporters cheered, reveling in a mix of nostalgia, patriotism and defiance. Some sang "God Save the Queen," while others embraced amid the smoke of fireworks.

On the white cliffs of Dover, the message: "The UK has left the EU" was projected between a British and an EU flag. 

The 10 Downing Street, the prime minister's office and residence, counted down to the 11 p.m. deadline with a light display. Government buildings in central London were lit up to celebrate the special occasion.

David Tucker, 75, said he had come to London from Wales to march in the hope that others would keep alive the prospect of one day rejoining the EU.

"It is a tragedy," he said. "We were once part of the world's most powerful economic bloc. Now we are just an inward-looking island that is going to get smaller."

Boris: This is an astonishing moment of hope

"For many people, this is an astonishing moment of hope, a moment they thought would never come," Prime Minister Boris Johnson, the New York-born leader of the official "Leave" campaign, said.

He celebrated in Downing Street with English sparkling wine and a distinctly British array of canapés including Shropshire blue cheese and Yorkshire puddings with beef and horseradish.

The EU's most powerful leaders, German Chancellor Angela Merkel and French President Emmanuel Macron, cast Brexit as a sad moment that was a turning point for Europe. The EU warned that leaving would be worse than staying.

U.S. President Donald Trump has long supported Brexit. U.S. Secretary of State Mike Pompeo said Britons wanted to escape the "tyranny of Brussels."

Uncertain future

Brexit was always about much more than Europe. The referendum exposed deep internal divisions and triggered soul-searching about everything from immigration to empire and modern "Britishness".

It has tested the very fabric of what now looks a disunited kingdom: England and Wales voted to leave but Scotland and Northern Ireland wanted to stay. The strains could hasten another referendum on Scottish independence and even a push for a united Ireland.

Opponents say Brexit is a folly that will weaken the West, torpedo what is left of Britain's global clout, undermine its economy and ultimately leave it a less cosmopolitan set of islands.

(With input from Reuters)