Brussels (AFP) - European Commission chief Jean-Claude Juncker on Friday warned countries not to go it alone in the wake of Brexit, as he marked the 25th anniversary of a summit that produced the Maastricht treaty.

Speaking in the Dutch town where EU leaders a quarter of a century ago hammered out a deal that gave birth to the euro, Juncker lashed out at those trying to "deconstruct" the crisis-hit bloc.

"Those who think the time has come to deconstruct the EU, to put the EU in pieces, to subdivide us into national divisions are totally wrong," former Luxembourg prime minister Juncker told an audience of students.

"We won't exist as single nations. We won't exist as a single country... In 20 years from now not one single member state will be member of the G7. Any questions?" he warned, referring to the G7 group of the world's richest nations.

Juncker said however that Britain's shock referendum vote to leave the EU showed that it could be time to develop a two-speed Europe, divided between countries that want more integration and countries that want less.

"The British feel too hot in the kitchen, they are not comfortable," he said. He began to talk about EU membership candidate Turkey, with whom relations are strained, but then broke off: "The Turks -- but this a president should not say."

"We have to invent a different orbit for those of our European countries who do not want to be part of all the domains where we are trying to work together. This would not be a tragedy, this would not be a crisis," he said.

Juncker -- who was Luxembourg finance minister at the time of the Maastricht summit and its only participant to still be politically active -- in theory has a double cause to party as Friday is his 62nd birthday.

But the anniversary of the Maastricht summit -- the treaty was officially signed on February 7, 1992 -- has been overshadowed by the EU's wave of problems, including the decision by Britain to split from the bloc.

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Juncker rebuked EU members that had broken the spirit of European unity during the migration crisis last year.

Eastern European countries such as Hungary and Slovakia have ignored a decision pushed through by Juncker's commission in 2015 to relocate refugees pouring into Greece and Italy across all the EU member states.

"That is something new -- for the first time in post-war European history not all the member states are applying the agreed rules," Juncker said.

"This is against this basic principle that the European Union is a rule-based system. It is no longer," he said.