Divisions over Europe's refugee crisis deepened on Thursday as record numbers of migrants streamed through the Balkans into Hungary, forcing Austria to suspend cross-border train services.
Germany, which is spearheading Europe's response to the emergency, warned that an EU plan to distribute 160,000 new arrivals among member states was a mere "drop in the ocean".
The plan already faces stiff opposition from eastern members, including those on the front line of the huge influx of people, who say they will not accept binding quotas from Brussels.
Foreign Minister Frank-Walter Steinmeier will try to win over eastern European states at a meeting in Prague on Friday.
The European Union is bitterly divided over how to cope with the biggest migrant crisis since World War II, with some countries on the bloc's borders hardening their stance while others in Western Europe have opened their doors.
Some 22,500 refugees and migrants arriving on the Greek island of Lesbos have been registered by officials since Monday evening, according to police, many of them Syrian refugees setting sail from Turkey.
In Hungary, police said Thursday 3,321 people had entered in just 24 hours, hurrying to cross before tough new anti-migrant laws take effect, a new border fence is completed, and the weather worsens.
Austria's train operator suspended services with Hungary on Thursday due to "massive overcrowding" and urged bus companies and volunteers to stop bringing migrants to stations.
In Serbia, where state television said 5,000 people had arrived at the border with Hungary, the prime minister warned the situation would worsen when new immigration laws come into force Tuesday.
'An accountancy exercise'
The UN refugee agency on Tuesday warned that at least 42,000 migrants were expected to enter Hungary by next week.
Many have endured treacherous sea journeys across the Mediterranean -- most fleeing war and poverty in Syria, Afghanistan or Pakistan.
On Macedonia's border with Greece, AFP journalists saw some 50 buses transporting some 2,500 migrants and three trains packed with 3,000 people departing from the town of Gevgelija.
EU interior ministers will meet Monday to discuss how to share the burden across the bloc and ease the pressure on frontline states.
Germany, which has already welcomed 450,000 migrants this year, wants the 28-nation group to go further, calling for no limits to the quotas.
"The distribution of 160,000 refugees across Europe is a first step, if one wants to be polite," said Deputy Chancellor Sigmar Gabriel. "It's a drop in the ocean."
But binding quotas are facing fierce resistance from eastern EU members.
"It is inappropriate to talk about mandatory quotas, calculated on an extremely bureaucratic basis, almost like an accountancy exercise I might say, without consulting member states," said Romania President Klaus Iohannis.
His views echoed those of Slovakian Prime Minister Robert Fico, who said Wednesday he did not "want to wake up one day and have 50,000 people here about whom we know nothing".
'Walking for hours'
Juncker's proposals include a possible revision of the EU's much-criticised Dublin Treaty, under which asylum claims must be processed by the first country where refugees arrive.
EU lawmakers called for an international conference on migration bringing together the United States, United Nations and Arab countries.
Facing criticism that his government has been too slow to help, US President Barack Obama pledged to admit at least 10,000 Syrian refugees in the year starting October 1.
Spokesman Josh Earnest said Obama had ordered staff to "scale up" the number of Syrian refugee admissions from around 1,500 this year after over 62,000 Americans signed a petition calling on Washington to take in more people.
Meanwhile, on the Greek island of Lesbos, another flashpoint in Europe's crisis, the boats kept arriving.
Hundreds -- perhaps thousands -- made a gruelling 50-60 kilometre walk from their landing place to the main town where they must go to receive registration papers.
"We have been walking for four hours. There is no bus, no taxi, no water, no anything," said Mohammed Yassin al-Jahabra, a 23-year-old English literature student.
Thousands of people have been forced to camp on the streets in squalid conditions, and there were repeated clashes as riot police struggled to control huge crowds pressing forward to get on board ferries.
But the boats are still arriving at an astonishing pace, with six landing in the space of an hour on Wednesday, AFP correspondents said.
"As soon as I put my feet down (on dry land), I stopped feeling tired," said Feras Tahan, a 34-year-old Syrian graphic designer, his shoes and trousers soaked.