Prime Minister Miro Cerar said he hoped a mini-EU summit with Balkan and central European leaders on Sunday would help bring solutions to the crisis, but he has not ruled out a barrier along the 670 kilometre frontier with Croatia.
"We are considering that option too but at this moment... we are still looking for a European option," Prime Minister Miro Cerar told state TV late Thursday.
Slovenia has become the main entry point into the European Union's passport-free Schengen zone after Hungary sealed its southern borders with razor-wire fences to stop migrants desperately trying to reach northern Europe before winter sets in.
Ljubljana has asked Brussels for €140 million, in addition to police backup and logistical support.
"If on Sunday we do not get sufficient (grounds for hope), if we see there is no will for collaboration, then all possibilities will are available, seeing as we will have been left alone," Cerar said.
But he stressed that he saw the fence as a last resort. "The border with Croatia is long and building a fence would be rather demanding. Police and army would have to guard it permanently to prevent illegal crossings," Cerar said.
More than 47,500 people have entered the small nation of two million people since October 17 when Budapest shut its frontier with Croatia, barely a month after also closing its Serbian border.
Most of the migrants, mainly fleeing violence in Syria, Iraq and Afghanistan, want to get to Germany, the EU's economic powerhouse.
Some 14,000 were waiting in Slovenian refugee camps and registration centres on Friday morning, hoping to continue to neighbouring Austria whose Spielfeld border camp was also bursting with new arrivals.
Austrian Foreign Minister Sebastian Kurz warned on Friday that the "surge into Europe" had become too big, adding that bloc members had a responsibility to protect their borders.
Border fences in Hungary and other EU countries had proven effective in tackling the crisis, Kurz said. "The question is whether you want them or not," he told public broadcaster Ö1.
His comments echo those of Interior Minister Johanna Mikl-Leitner who on Thursday announced it was time for the EU to "build fortress Europe", after she had visited the Spielfeld checkpoint.
Some 7,000 refugees have crossed into Austria from Slovenia since Thursday, with some 4,500 still stranded at Spielfeld on Friday morning, police said.