The huge influx of migrants from Syria and Iraq is putting the future of the European Union in "grave danger", French prime minister Manuel Valls has warned.
Mr Valls said that European societies could be "totally destabilised" unless the EU imposes tighter controls at its external borders and makes clear it will not accept all of the refugees seeking to enter the continent.
If the EU cannot control its external borders, the Schengen arrangement of border-free travel between most of the 28 member-states - but not the UK - will be thrown into doubt, he said.
But he made clear that the threat from the migration crisis runs much deeper, telling the BBC: "It's Europe that could die, not the Schengen area. If Europe can't protect its own borders, it's the very idea of Europe that could be thrown into doubt.
"It could disappear, of course - the European project, not Europe itself, not our values, but the concept we have of Europe, that the founding fathers had of Europe.
"Yes, that is in very grave danger. That's why you need border guards, border controls on the external borders of the European Union."
In an interview at the World Economic Forum in Davos, Switzerland, Mr Valls said that German Chancellor Angela Merkel had shown "courage" in announcing last year that her country would welcome thousands of refugees.
But he left little doubt that he believed her message was wrong, and had played a role in encouraging refugees to travel to Europe in the hope of a new life.
He made a pointed reference to the New Year's Eve sex attacks in the city of Cologne, which have been blamed on recent migrants, as he said that the arrival of thousands of migrants presented "a major challenge" to Germany.
"We need to help Germany," said the French PM. "But the main message we must send now with the greatest of firmness is to say that we will not take in all the refugees in Europe.
"A message that says 'Come, you will be welcome' provokes major shifts of population. If you say anything in Europe today, a few seconds later it is on the smartphones of people in refugee camps near Libya.
"Angela Merkel showed courage. She explained why she wanted to welcome the refugees in the name of values, and also because Germany needs these refugees.
"But we know clearly that after the Cologne incidents that with the continuous flow, not only to Germany but other countries of Northern Europe, Austria and the Balkans are confronted with this influx, that's why we need to find practical solutions for our borders."
Mr Valls said that ending the migration crisis would have to involve solutions to the wars raging in Syria and Iraq, the destruction of the Islamic State terror group - also known as Daesh, Isil or Isis - and the establishment of a new political process in Syria.
But he said that these processes will "take time", and that there was an urgent need for tighter border controls, as well as more reception centres for migrants arriving in Greece and Italy and assistance for refugee camps in Jordan, Lebanon and Turkey.
"We cannot say nor can we accept that Europe can take in all the refugees, all of those fleeing these terrible wars in Iraq or Syria," said Mr Valls.
"Otherwise our societies will be totally destabilised ...
"We need border controls at the external borders of the European Union, because Europe has forgotten that it needs borders."
He added: "Sometimes we had the idea that borders did not exist. But, no, borders do exist. We must protect our borders. If they are not protected, then we will reimpose - as we have done - internal European border controls, and then the Schengen area is thrown into doubt.
"If we start to question the free movement of people, then one of the great European projects is also thrown into doubt."