Brussels (dpa) - The European Union woke up Friday to a political earthquake, with Britain's decision to leave the bloc heralding years of uncertainty, not only for the country but for the fate of the entire European project.
"It looks as though Europe's worst nightmare has become true," ING Bank analyst Carsten Brzeski wrote ahead of the official result. "A long, difficult and dirty divorce process lies ahead."
"This is a bitter day for Europe," said German Foreign Minister Frank-Walter Steinmeier. "We had hoped until the end that the citizens of Britain would decide differently."
Britain's departure - a process expected to take at least two years to unpick 43 years of marriage - will leave the remaining 27-member EU stripped of its second-largest economy, one of its two nuclear powers and one of its two UN Security Council veto-holders.
But what many governments fear more is the impact of Brexit on the fabric of the bloc, as eurosceptics across the continent celebrated Friday's referendum outcome.
"We are determined to keep our unity as 27," EU President Donald Tusk said early Friday. "I am fully aware of how serious, or even dramatic, this moment is politically," he added.
Asked by a journalist whether Britain's decision was the beginning of the end for the EU, European Commission President Jean-Claude Juncker - looking drawn and downcast - responded with a firm "no."
The referendum has come at a time when the EU is facing a series of crises, from last year's migration surge to tensions with Russia and persistent economic challenges, while many are rejecting the medicine prescribed by Brussels to stimulate growth and job creation.
Eurosceptic party leaders Marine Le Pen in France and Geert Wilders in the Netherlands called Friday for their countries to follow Britain's example, while anti-establishment parties in Austria, Italy and Spain have grown strong on demands for fundamental change in Europe.
On Friday, European politicians were scrambling to respond to these calls.
"A jolt is necessary," French President Francois Hollande wrote on Twitter. "To move forward, Europe can no longer continue as before."
"This is an alarm bell for the EU and we'll have to bring the European project closer to European people," added Slovak Foreign Minister Miroslav Lajcak. His country is about to take over the EU's rotating presidency.
"Without adaptation, ... we risk that we will lose another country, one or two in the coming five or six years," said Polish Minister for European Affairs Konrad Szymanski.
"I can guess what it is that people demand of us," Steinmeier said. "They want to see that the EU is able to resolve the problems that people are feeling."
Some have argued that the departure of Britain - a country that had applied the brakes on further European integration - will be a chance for the bloc to grow together and embark on ambitious reforms, for instance on efforts to achieve closer economic alignment.
But this is unlikely, argued Karel Lannoo of the Centre for European Policy Studies think-tank.
"Most politicians and most member states will interpret this [vote] as a sign that political integration has gone too far," he said.
"The Brexit negotiations will clog up the EU's agenda for the coming months and years, making it less likely that the EU is able to tackle the reforms needed," analysts Fabian Zuleeg and Janis Emmanouilidis wrote for the European Policy Centre.
Meanwhile, some said that Brexit could provide new opportunities.
"Today is a new beginning and it's up to us to make the best out of it, for all Europeans," Slovak Finance Minister Peter Kazimir wrote on Twitter.
"I'm stirred, not shaken," added Danish Foreign Minister Kristian Jensen. Although Denmark has often been compared to Britain for its lacklustre approach to the EU, his country knew it was stronger within, Jensen added.