Hungarian police clashed Wednesday with several hundred migrants furious at being blocked from crossing the border with Serbia, as desperate refugees opened up a new route into Croatia to get round Budapest's razor-wire barrier.
Authorities fired tear gas and deployed water cannon to quell what they said was an "aggressive" crowd of some 500 people, as police helicopters buzzed overhead.
Earlier Wednesday, Croatia granted free passage to migrants desperate to find new ways to western Europe after Hungary sealed its frontier and EU states tightened border controls over the unprecedented human influx.
At dawn, a small group of women and children crossed cornfields into Croatia from Serbia, followed shortly afterwards by around 370 mostly Syrians and Afghans, according to an AFP correspondent at the scene.
Croatia said it was expecting another 4,000 people in coming days.
Pressure is building for a special EU summit to come up with solutions to the continent's worst migration crisis since World War II, with the bloc bitterly split and free movement across borders -- a pillar of the European project -- in jeopardy.
Croatian Prime Minister Zoran Milanovic -- who has blasted Hungary's border fence as "unacceptable" -- said all migrants could pass through the EU state, allowing them to push on towards Slovenia, Austria and Hungary's fenceless southwestern frontier.
"We are ready to accept and direct those people, their religion and colour of skin is completely irrelevant, to where they apparently wish to go -- Germany and Scandinavia," Milanovic told lawmakers.
But his Slovakian counterpart Robert Fico added to the war of words between EU capitals by warning Europe was at risk from what he called a "migrant onslaught".
"The EU has found itself under the onslaught of hundreds of thousands of migrants and has ceased to be a safe place," the leftist leader told parliament, insisting that "90 percent of these people are economic migrants."
- 'Hungary is closed' -
"We heard that Hungary was closed so the police told us we should come this way," Amadou, 35, from Mauritania in west Africa, told AFP as he walked towards the Croatian frontier -- which is still peppered with minefields from the Balkan wars of the 1990s -- from the Serbian border town of Sid.
Hungary's conservative Prime Minister Viktor Orban is also planning a new fence along the frontier with Romania, prompting outrage from its southern neighbour.
But Budapest insisted the barrier was working as it made its first arrests under tough new laws which punish "illegal border-crossing" with prison terms of up to three years.
Germany The controversial measures are part of Orban's strategy to stem the flow of migrants trudging up through the western Balkans, most headed to Germany and Sweden.
The result was plain to see in statistics released by Hungarian police on Wednesday, with the number of people intercepted falling to just 367 from a record 9,380 the day before.
The apparent success in deflecting the flow sparked fears in Serbia that it would be swamped by an unmanageable number of migrants.
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Speaking to AFP at the Horgos crossing, Serbia's minister for refugees, Aleksandar Vulin, called on Hungary to reopen the border "at least for women and children" as around 100 people waited in vain to cross.
- Domino effect -
From the Alps to Istanbul, thousands of other migrants were caught in similar bottlenecks, with hundreds setting out to walk to Germany from the Austrian border city of Salzburg after trains north were suspended as Berlin reintroduced border controls.
Germany, Austria and Slovakia have introduced identity checks on parts of their borders, and Poland and the Netherlands are considering whether to follow suit.
The measures have caused tailbacks at road crossing points and stoked concern among German road hauliers, who point to rising costs.
And hundreds more were stranded in the Turkish border city of Edirne after police stopped around 1,000 refugees from crossing into Greece and Bulgaria.
And huge crowds were camped out at Istanbul's main bus station for a second night running, after being refused tickets to Edirne.
"They cannot stay here. Maybe we will allow them to stay two or three days but then they have to leave," Edirne governor Dursun Ali Sahin told Turkey's NTV channel.
Hungary's hardline anti-immigration stance has been sharply criticised, with the UN refugee agency saying it could violate the 1951 Refugee Convention.
Romania, which is a member of the EU but not of the passport-free Schengen zone, criticised Hungary's planned border fence as "out of step with the spirit of Europe".
- Another blow to Schengen -
Politically, though, the big concern is for the future of the 20-year-old Schengen agreement, considered as important as the euro by many EU supporters.
By doing away with border checks and reducing bureaucracy, it provides a powerful economic stimulus and enhances a common European identity, they say.
Berlin's decision Wednesday to extend greater passport controls to its border with France -- the Schengen zone's other principal architect -- seemed to deal it another blow.
German Chancellor Angela Merkel and her Austrian counterpart Werner Faymann on Tuesday called for a special EU summit next week to debate the crisis.
"Time is running out," Merkel warned, urging an end to the squabbling that has flared since eastern members flatly refused to accept EU-set quotas for taking in tens of thousands of refugees.
European President Donald Tusk will announce a decision about the summit on Thursday, with EU interior ministers to meet again Tuesday in a fresh bid to resolve the quota wrangle.