EU leaders have insisted that the UK must move swiftly to negotiate leaving the organisation, saying any delay would prolong uncertainty.

European Commission head Jean-Claude Juncker stressed the "Union of the remaining 27 members will continue".

The UK voted by 52% to 48% to leave the EU, and David Cameron has announced he will step down as PM by October.

He has said it will be up to the new PM to invoke the article that will begin the UK's withdrawal.

Global stock markets fell heavily on the news of the so-called "Brexit" and the value of the pound has also fallen dramatically.

Mr Juncker went into crisis talks with European parliament president Martin Schulz, president of the European Council Donald Tusk and Dutch PM Mark Rutte on Friday morning.

They then released a statement saying they regretted but respected the British decision.

They called for the UK "to give effect to this decision of the British people as soon as possible, however painful that process may be. Any delay would unnecessarily prolong uncertainty".

They said: "We stand ready to launch negotiations swiftly with the United Kingdom regarding the terms and conditions of its withdrawal from the European Union."

They added that the deal agreed with Mr Cameron in February to protect London's financial markets, curb immigration and opt out of closer union "ceases to exist" and "there will be no renegotiation".

The sense of shock is palpable. EU leaders are struggling to come to terms with a huge setback for those who believe in the idea of European unity. The EU will never be the same again without the UK.

It is also clear the leaders want negotiations on a political and economic divorce to move swiftly. That means they want the UK to invoke Article 50 of the Lisbon treaty - the mechanism under which separation will be negotiated - as soon as next week, rather than wait for a new British prime minister in October.

In other words, tensions are already coming to the surface. And even though all sides are emphasising the need for co-operation, in many capitals there will be little appetite for doing the UK any favours.

Europe's political order has been overturned - with far-reaching consequences that no-one can accurately predict.

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The leaders also said that while the UK remained in the EU, it must abide by "all the rights and obligations that derive from this".

The UK must invoke Article 50 of the Lisbon Treaty to leave, which then allows for two years for withdrawal to be negotiated.

Mrs Merkel expressed "great regret" at the outcome of the vote

Some EU politicians fear a domino effect from Brexit that could threaten the whole organisation.

Polish President Andrzej Duda said everything possible must be done to prevent other countries leaving.

Leaders of Eurosceptic parties in France, the Netherlands and Italy quickly demanded referendums in their own countries.

Reacting to the vote, UK Independence Party leader Nigel Farage said "the EU is dying".

But Mr Tusk said this was "not a moment for hysterical reactions".

Although many EU leaders expressed shock and dismay at the vote, they also urged solidarity and some stressed the need for change.