Ljubljana - Europe's worst migration crisis since World War II risks triggering "tectonic changes", a top EU official warned Tuesday, as figures showed more than 700,000 newcomers have reached the continent's Mediterranean shores this year.
"The situation will deteriorate even further," European Council president Donald Tusk said, warning of a "new wave of refugees (arriving) from Aleppo and other Syrian regions under Russian bombardment".
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"I have no doubt that this challenge has the potential to change the European Union we have built," he told the European Parliament in Strasbourg.
"And what is even more dangerous, it has the potential to create tectonic changes in the European political landscape. And these are not changes for the better."
European Commission president Jean-Claude Juncker meanwhile slammed EU member states for providing less than half of the guards pledged to the bloc's Frontex border agency in migrant hotspots Greece and Italy.
"Member states have been moving slowly at a time when they should be running," he said.
Of the 775 border guards needed, EU countries have only provided 326 over the past month, Juncker said, adding that many bloc members had also failed so far to keep their promises of financial support.
The stinging criticism came just days after the EU vowed to help set up 100,000 places in reception centres in Greece and along the migrant route through the Balkans.
The move is part of a 17-point action plan devised with the countries most affected by the crisis.
German Chancellor Angela Merkel and French President Francois Hollande held talks on the crisis in Paris on Tuesday, with a French official saying afterwards the two shared "the same position on what should be done politically and on the measures required for the countries on the front line".
- Worsening weather -
More than half of this year's arrivals in Europe were from Syria, followed by Afghanistan and Iraq, the UN refugee agency said Tuesday.
Some 562,355 people desperately fleeing war and misery reached Greece's shores, while around 140,000 arrived in Italy since January.
At least 3,210 people have either died or gone missing while making the perilous journey in flimsy boats.
The flow shows no sign of abating despite the rapid approach of winter, according to the International Organization for Migration, which reported the arrival of more than 9,000 people in Greece over the weekend.
In Sweden, a group of migrants are locked in a standoff with authorities, saying the village where they have been taken is "too cold" and isolated, officials said Tuesday.
Around 60 Syrians and Iraqis were taken by bus on Sunday to Limedsforsen, close to the Norwegian border, where they were to stay while their asylum claims were assessed.
But around a third refused to get off the bus when they saw they were in a forest dozens of kilometres from the nearest town. Many demanded to be taken to a big city -- or even to Germany.
As a majority of migrants seek to reach northern Europe, the influx has overwhelmed countries along the migrant trail up from Greece through the Balkans, and sparked concern that the EU's cherished "Schengen" system of borderless travel is under threat.
More than 83,600 people have arrived in Slovenia since mid-October after Hungary shut its Croatian border with a razor-wire fence, police said Tuesday.
Tiny Slovenia, which has a population of just two million, reiterated its warning that it is also considering building a fence if the newly-announced EU plans aimed at tackling the crisis fail to produce quick results.
"If the situation worsens and the Brussels action plan is not fulfilled, then Slovenia has several scenarios prepared, (including) the installation of a fence guarded by forces," said Slovenian Foreign Minister Karl Erjavec.
Border pressures have prompted sharp exchanges between Slovenia and Croatia in recent days, with each accusing the other of failing to properly manage the influx.
Tensions have been rising in particular in the Slovenian border village of Rigonce, where residents are increasingly disgruntled at the sight of thousands crossing from Croatia.
Further north, the relentless wave of arrivals also sparked tensions between Austria and the neighbouring German state of Bavaria, which on Tuesday accused Austrian border police of waving thousands of migrants through without informing local authorities.
Austrian police rejected the claim, instead blasting Bavarian security forces for only processing up to 50 migrants an hour.
Austrian police spokesman David Furtner described the move as "a joke" that risked creating a dangerous bottle-neck.