The move comes a month after Hungary's right-wing government shut its frontier with Serbia to hundreds of thousands of migrants, many of them refugees from war in Syria, streaming across the Balkan peninsula from conflict and poverty in the Middle East, Africa and Asia.
Hungary has erected a steel fence almost the length of its southern frontier, declaring it has to secure the borders of the European Union from mainly Muslim migrants who it says pose a threat to the prosperity, security and "Christian values" of Europe.
The flow continued unabated on Friday over the border of EU neighbours Croatia and Hungary - between 5,000 and 8,000 per day in recent weeks, picked up by bus on the Hungarian side and driven north to Austria. The vast majority are trying to reach Germany.
With winter approaching and temperatures dropping, they now face being diverted from Croatia into Slovenia, like Hungary a member of Europe's Schengen zone of passport-free travel.
Croatia said it had agreed a plan with fellow former Yugoslav republic Slovenia to handle the flow of migrants when Hungary sealed the border. Slovenia denied this but confirmed that the neighbours were holding "operational talks".
Slovenia, a country of 2 million people, said it would designate one or two entrance points for migrants and convene its national security council on Saturday.
Foreign Minister Karl Erjavec indicated that Slovenia would not restrict entry providing Germany keeps its doors open.
"If Germany closes its border or restricts border crossings, then Slovenia will act accordingly. But so far there are no indications or information that Germany is to change its policy," Erjavec told a news conference.
The EU has agreed a deal - resisted by some of its members in eastern Europe - to share out 120,000 refugees, only a small proportion of the 700,000 or so people expected to reach Europe this year.
