The leaders of Austria, Bulgaria, Croatia, Germany, Greece, Hungary, Romania and Slovenia will meet their counterparts from non-EU states Macedonia and Serbia on Sunday, the office of European Commission President Jean-Claude Juncker said.
"In view of the unfolding emergency in the countries along the western Balkans migratory route, there is a need for much greater cooperation, more extensive consultation and immediate operational action," a statement said.
More than 600,000 migrants and refugees, mainly fleeing violence in Syria, Iraq and Afghanistan, have braved the dangerous journey to Europe so far this year, the UN said.
The goal for many travelling along the western Balkan route is the EU's biggest economy Germany, which expects to take in up to one million refugees this year.
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Since Saturday, when Hungary sealed off its border with Croatia, more than 21,455 migrants have arrived in Slovenia, a nation of two million people.
In response to the crisis, Prime Minister Miro Cerar yesterday asked the EU for backup from police forces in other EU countries and extra equipment for its own officers.
Under the measures, soldiers can detain people and hand them over to police, as well as issue orders to civilians in the border area.
"The last 24 hours have been the toughest and most demanding since the start of the crisis," the Slovenian government said, warning it was "delusional" to expect small countries to succeed where larger ones had failed.
EU Commissioner for Migration Dimitris Avramopoulos is expected to visit Slovenia on Thursday to discuss the request.
There were reports of brief tensions between migrants and police in the country's biggest refugee camp near the Austrian border.
Meanwhile, several hundred more migrants were waiting in cold weather near the Croatian border to cross into Slovenia this morning, an AFP reporter said.