Thousands of migrants, mostly Syrian refugees, travelled through Macedonia and Serbia on Sunday towards western Europe, as Italy's foreign minister said the escalating crisis threatened the bloc's "soul".
More than 7,000 men, woman and children crossed into southern Serbia from Macedonia overnight Saturday to Sunday alone, the UN's refugee agency (UNHCR) said, with many more still expected to arrive.
The mass movement came after Macedonian police on Saturday finally re-opened the border with Greece after three days of trying to hold back streams of migrants.
Macedonia had on Thursday declared a state of emergency and sealed off its border to halt the influx, leaving thousands stranded in no-man's land.
After a tense standoff on the border, hundreds of stranded refugees, many carrying small children, forced their way through barbed wire fences in dramatic scenes on Saturday as police hurled stun grenades.
By Saturday evening, border guards stood aside to allow 1,500 migrants through unhindered, with many heading straight for Serbia, the next stop on their journey to reach the European Union.
The UNHCR said Sunday it had received assurances from the Macedonian government "that the border will be open to refugees fleeing conflict in their countries of origin".
On the Serbian side of the frontier, the UN agency said it was working with local authorities and charities to provide shelter and food for the new arrivals, but that more supplies were needed, including "sleeping mats, blankets, tents and accommodation halls".
Eight huge UN refugee agency tents were set up in the border village of Miratovac, where people were visibly exhausted and many asked for medical aid. There were many children and pregnant women among them, an AFP photographer said.
Buses were being laid on to the nearby town of Presevo where police handed out documents and helped the migrants take buses to their next destination, the border with Hungary.
Unlike Serbia, Hungary is an EU member state and therefore a popular crossing point into the bloc, although the country is currently building a four-metre (13-foot) barbed wire fence along its 175-kilometre border to stop the influx.
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- Germany's 'biggest challenge' -
Faced with what the bloc has called its worst refugee crisis since World War II, German Chancellor Angela Merkel and French President Francois Hollande will hold talks in Berlin on Monday in a bid to give a fresh impetus to the EU's response in dealing with the situation.
The leaders will discuss their countries' wish "to go much further in harmonising" strategy on several aspects including asylum policies, a French presidency source said.
Nearly 340,000 migrants have arrived in the EU in the first seven months of this year, according to the bloc's Frontex border agency.
In Geneva, the International Federation of Red Cross and Red Crescent Societies (IFRC) said "greater levels of collaboration and collective effort are necessary in order to manage the humanitarian needs of those affected".
In Rome, Italian officials said the coastguard had rescued 4,400 migrants from 22 boats in the Mediterranean on Saturday, in what was understood to be the highest daily figure in years.
More than 108,000 people have arrived in Italy alone this year, prompting Foreign Minister Paolo Gentiloni to warn that the deepening crisis could pose a major threat to the "soul" of Europe.
"On immigration, Europe is in danger of displaying the worst of itself: selfishness, haphazard decision-making and rows between member states," Gentiloni told Il Messaggero.
In Germany, Vice Chancellor Sigmar Gabriel said a four-fold increase in asylum requests -- expected to top 800,000 this year -- was the country's "biggest challenge since reunification" in 1990.
He and Foreign Minister Frank-Walter Steinmeier issued a joint call Sunday for Europe to "fairly" share out the refugees and urged the creation of a "European asylum code".