AFP/ Presevo

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".

The mass migration of more than 6,000 people, according to Red Cross figures, came after Macedonian police finally re-opened the border with Greece on Saturday, allowing thousands to travel north towards Serbia in the next stage of their bid to enter the European Union.

Macedonia had on Thursday declared a state of emergency and sealed off its southern 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.

By mid-Sunday, more than 6,000 refugees and migrants had crossed into Serbia where eight huge UN refugee agency tents were set up in the border village of Miratovac.

Amet Alimi, president of Presevo's Red Cross branch, told AFP: "We have worked all night to admit them. There is a flow of people who keep coming."

People were visibly exhausted and many asked for medical aid. There were many children and pregnant women among them, an AFP photographer said.

They were being bussed to the nearby town of Presevo where police handed out documents and helped them take buses to the border with Hungary, which unlike Serbia is an EU member state.

- Crossing freely -

In Gevgelija, on Macedonia's southern border with Greece, refugees and migrants kept coming, hundreds at a time.

They waited for trains to take them on to Serbia while some haggled with taxi drivers to make the 180-kilometre (110-mile) journey, often for exorbitant sums.

"It's been madness throughout the night with people everywhere, buses coming and going and taxis arriving from other towns," a taxi driver who identified himself as Milan said.

More than 400 were in no-man's land, patiently waiting to be allowed in, an AFP reporter said.

Rostom Mohamed arrived in Greece after travelling from Iraq with his wife and three children. He said they had paid 4,000 euros ($4,550) to smugglers for a boat transport from Turkey to Greece, adding that "three people died on the way".

"I want to go to Germany for work. I want to be safe and live like a human being. That's why I choose to come to Europe," he said, as his family was waiting to enter Macedonia and continue northwards to the EU.

Police had previously said they would only admit "a limited number" of people but they were not making any attempt to stop those crossing, the correspondents said.

Once the migrants reach Serbia, many try to make their way to Hungary, which is a major crossing point into the EU, although the country is building a four-metre (13-foot) barbed wire fence along its 175-kilometre border to stop the influx.

- Germany's 'biggest challenge' -

Europe is struggling with a huge influx of migrants in what the EU has described as its worst refugee crisis since World War II.

Official figures show a record 107,500 migrants crossed into the EU last month and the figure looks set to increase.

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.

The number raises to more than 108,000 the number that have arrived in Italy alone this year, prompting Foreign Minister Paolo Gentiloni to warn that the deepening immigration 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.

And in Germany, Vice Chancellor Sigmar Gabriel said a four-fold increase in asylum requests was the "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" that would guarantee bloc-wide asylum status.