German Chancellor Angela Merkel and her Austrian counterpart, Werner Faymann, have issued a joint call for an emergency EU summit to address the refugee crisis.
"This is the most difficult situation Europe has faced for decades," Mrs Merkel said in a joint press conference in Berlin.
"I say again and again, we will master the situation, but the challenges can only be faced together."
Mr Faymann invoked the spectre of the rise of Nazism as he made it clear that in his view the stakes could not be higher for Europe.
"We must not look the other way if there is a humanitarian crisis in Europe," he said.
"If we do that, we will endanger the European project in the hearts of the people of Europe.
"We mastered the danger in the financial crisis and we proved that we could prevent a return to the solutions of the 1930s. That is what we must continue to do now."
The two leaders said they had formally requested Donald Tusk, the European council president, to call a special summit as early as next week.
Mrs Merkel appeared to reject suggestions from her interior minister that funding should be cut to Eastern European countries blocking plans to distribute refugees by quota.
"Threats are not the right way to go," she said.
But in criticism clearly aimed at Hungary and its hardline leader Viktor Orban, she also said: "We cannot pass this problem to the people next door."
Ms Merkel reiterated Germany's commitment to give shelter to genuine refugees.
"If we end up rejecting help to those people who have been recognised as refugees, then I cannot accept that," she said.
But she emphasised that all EU members have already agreed to give asylum to those in genuine need, and made clear that she expected her EU partners to live up to their commitment.
But even as she was speaking, Hungary announced that it will build a fence along part of its border with Romania to ensure migrants and refugees can be kept out of the country, the country's foreign minister has said.
Peter Szijjarto said the fence would be built in addition to the one that has been built along the Serbian border.
"The government has decided to make preparations for the construction of a fence on the Hungary-Romania border, extending from the border triangle of Hungary, Serbia and Romania, for a reasonable distance," Mr Szijjarto told a press conference in the capital.
The announcement came as Sweden's King Carl XVI Gustaf called Europe's migrant crisis "a tragedy that has touched us all."
Speaking at the opening of parliament after the summer recess, he stressed the country's traditions of tolerance and humanitarianism.
"Let us seize on this feeling and try to find ways to help people in need," the 69-year-old king said in a speech. Meanwhile, Croatia has said it fears that migrants and refugees will come to the country after Hungary closed its border with Serbia.
"It is a system of spilling over ... if they (refugees) cannot go somewhere, there is a realistic possibility that they will head in our direction," said Zlatko Sokolar, head of border administration.
Yesterday, declaring a state of emergency, Hungary sealed off its southern border with Serbia and detained those trying to enter illegally, aiming to shut down the flow of refugees pouring in.
Chaos ensued at the border, as hundreds of refugees piled up in a no-man's land, and Serbian officials reacted with outrage.
Stuck for an unknown amount of time on a strip of road between the two countries' checkpoints, those fleeing violence in their homelands pitched tents and settled in.
But frustrations were on the rise. As a police helicopter hovered above, refugees chanted "Open the border!" and shouted insults at Hungarian riot police. Some refused food and water in protest.
Both Serbian and Romanian governments decried Hungary's moves to extend the razor-wire fence - which has already been completed along the Serbian border - to the border with Romania. (© Daily Telegraph, London)