The EU's migration commissioner is to visit new hotspot Slovenia on Thursday to discuss its urgent call for help as the small nation buckles under a record surge of refugees desperate to reach northern Europe before winter.
Slovenia is now the main entry point into the passport-free Schengen zone, with tens of thousands arriving after Hungary sealed its key southern borders with razor-wire fence.
The visit came as the UN rights chief accused neighbouring Czech Republic of systematically detaining migrants and refugees in "degrading" conditions, as part of a policy to dissuade them from entering the country.
The continent has been struggling to find a unified response on how to tackle its biggest migration crisis since World War II.
More than 600,000 people, mainly fleeing violence in Syria, Iraq and Afghanistan, have braved the dangerous journey to Europe so far this year, the UN says.
Of these, over 3,000 have drowned or gone missing in the Mediterranean.
Many have set off from Turkey in inflatable boats to Greece, the main starting point for a long trek north through the Balkans and central Europe.
The goal for most is the EU's biggest economy Germany, which has eased asylum restrictions and expects to receive up to a million requests this year.
While many in Germany have welcomed the migrants, there has also been a backlash, with 576 offences targeting refugee hostels since the start of the year, 523 of which were committed by far-right extremists, police said.
Chancellor Angela Merkel was to address a gathering of EU conservative parties in Madrid on Thursday, along with Hungarian Prime Minister Viktor Orban, known for his hardline stance on refugees.
- Freezing cold and fog -
More than 12,600 people streamed into Slovenia -- a nation of two million people -- within 24 hours, police said Thursday.
This brings the total number of arrivals to 38,587 migrants since Saturday when Budapest sealed its frontier with Croatia, just a month after closing its border with Serbia.
As Ljubljana struggles to cope, EU Commissioner for Migration Dimitris Avramopoulos was set on Thursday to discuss possible backup from police in other EU countries and financial assistance.
Over 10,000 people were in Slovenian registration centres on Thursday morning hoping to continue their journey to Austria, whose Spielfeld border camp was also bursting with new arrivals.
Further south, long queues continued to form at Slovenia's border with Croatia.
A train carrying 2,000 migrants arrived at the Dobova railway border crossing on Thursday, an AFP reporter said.
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Amid heavy police presence, the exhausted travellers -- some wearing only sandals -- slowly shuffled into Slovenia while an army helicopter circled over their heads.
Many of the migrants' clothes were covered in mud after a cold, exhausting journey through Greece, Macedonia and Serbia.
A 27-year-old Syrian said he and his wife had fled the spiralling conflict in Damascus 10 days ago, shortly after getting married.
"We sold everything, we don't have a life there anymore," he told AFP.
Several hundred people also stood shivering in cold weather and fog at the Berkasovo checkpoint, near Croatia's border with Serbia, on Thursday, an AFP reporter said.
The crowd chanted "Open! Open!" as Croatian police only allowed a trickle of people through every 15 minutes.
Many migrants had spent the night in makeshift tents on the roadside, with temperatures plunging close to zero Celsius degrees (32 F).
- 'Immediate action' needed -
In view of "the unfolding emergency" in the region, the European Commission called a mini-summit with Balkan leaders on Sunday, acknowledging there was "a need for much greater cooperation... and immediate operational action".
With at least 9,000 people landing on Europe's beaches every day, even wealthier bloc members insisted the influx was stretching reception capacities beyond limits.
Sweden said Thursday it expected up to 190,000 asylum applications this year, warning that it already lacked housing available for up to 45,000 of recent arrivals.
EU conservative parties meeting in Madrid called for a strengthening of the bloc's external borders, warning that the influx risked destabilising the continent.
But EC chief Jean-Claude Juncker insisted Europe had a duty to help the migrants.
"I don't often cry but when I see, night after night, this long procession of refugees which reminds me of images from the end of World War II ... it almost makes me cry," he said Wednesday.
Last month, the EU approved plans to relocate 160,000 asylum seekers from overstretched frontline states Italy and Greece with a compulsory quota system that was fiercely opposed by some eastern, more hardline members of the bloc.
The proposal requires most of the 28 member states to accept a share of the refugees over the course of two years.
Member states have been slow to follow up with promised financial help -- out of the 2.8 billion euros ($3.2 billion) pledged at an emergency EU summit on September 23, only about 474 million euros has materialised.
The Turkish government this week warned it was bracing for a new mass exodus from neighbouring Syria amid escalating violence there.