VIENNA (AFP) - Austria said on Wednesday (Oct 28) it would build a fence along its border with fellow European Union state Slovenia to "control" the migrant influx, in what would be the first barrier between two members of the passport-free Schengen zone.

Both countries have become key transit points for tens of thousands of refugees and migrants seeking to reach northern Europe ahead of the winter, and before more potential EU border closures.

Vienna's announcement prompted sharp criticism from Berlin amid an escalating spat over Austria's handling of the humanitarian drama.

"We do not believe that the current migrant crisis that Europe is facing can be resolved with the building of fences or walls," said German government spokesman Steffen Seibert, adding that the problem could only be dealt with if countries stood united.

The small Alpine nation of Slovenia, which has been swamped by migrants recently, also reiterated its readiness to erect a fence along its Croatian frontier if new EU plans aimed at improving the situation failed to produce quick results.

Austria's move is bound to intensify concerns about the EU's cherished Schengen system, a crucial part of European integration efforts, which allows for the free movement of people and goods.

But Interior Minister Johanna Mikl-Leitner insisted the planned barrier was "not about shutting down the border".

"This is about ensuring an orderly, controlled entry into our country. Also, a fence has a gate," she told Austrian media Wednesday.

Big rifts have opened up between EU members over how to handle Europe's worst refugee crisis since World War II.

More than 700,000 migrants and refugees have already landed on the continent's southern shores so far this year, the majority from Syria, Iraq and Afghanistan.

The endless procession has overwhelmed nations along the migrant trail leading from Greece through the Balkans, already prompting Hungary - also an EU and Schengen member - to seal its southern borders with razor wire.

- 'Fortress Europe' -

The EU said Wednesday it had "not been notified" of Vienna's decision to build a fence.

European Commission President Jean-Claude Juncker was to meet Austrian Chancellor Werner Faymann later Wednesday to discuss the situation, EU spokeswoman Natasha Bertaud told AFP.

The decision comes just days after Juncker and other EU leaders at an emergency Balkans summit warned that "unilateral actions could trigger a chain reaction".

Few details have been released so far about the planned barrier, which is set to run several kilometres either side of the Spielfeld border crossing, where thousands of migrants have arrived in recent weeks.

Mikl-Leitner - who last week said it was time to build "fortress Europe" - stressed Wednesday the situation risked escalating as migrants grow "more impatient and aggressive" over being forced to wait in cold weather for hours before being allowed to cross from one nation into another.

Refuting claims that the fence risked creating human bottlenecks, Mikl-Leitner pointed the finger at Germany, saying border police there processed "too few migrants".

She also implicitly criticised Chancellor Angela Merkel's open-door policy.

"The fact is that the majority want to go to Germany, because they feel they have been invited," Mikl-Leitner said.

- Afghans told to stay home -

Her German counterpart Thomas de Maiziere hit back, accusing Austrian border police of waving through thousands of migrants without properly informing local authorities.

"Austria's behaviour in the past few days has not been okay," he said Wednesday, adding the two neighbours were "in constant contact" to solve the situation.

Germany, the EU's economic powerhouse, is expecting up to one million asylum-seekers this year, with Afghans making up the second-largest group after Syrians.

De Maiziere on Wednesday warned that the rising number of Afghans was "unacceptable", urging them to stay at home and rebuild their homeland.

Thousands of people from the Balkans, who had had their German asylum requests rejected, would also be returned to their countries in the coming weeks, he said.

Further down the migrant trail, Slovenia has seen nearly 90,000 migrants pass through since mid-October, when Budapest sealed its frontier with Croatia.

Buckling under the strain, the nation of two million people warned it too would shut its border if the EU did not stick to a 17-point action plan announced at Sunday's Balkans summit.

"As a European I do not desire (a fence) but the state will be forced into it if the commitments (from Brussels) are not fulfilled," Prime Minister Miro Cerar said Wednesday.

As part of the plan, the EU has pledged to send 400 police officers from other bloc members to Slovenia. It has also vowed to set up 100,000 places in reception centres in Greece and the Balkans.

Juncker has slammed EU member states for providing less than half of the guards pledged to the bloc's Frontex border agency in migrant hotspots Greece and Italy.

"Member states have been moving slowly at a time when they should be running," he said Tuesday.