Large numbers of soldiers and police were at the scene, some guarding construction equipment, a Reuters photographer there said.
Slovenia is the smallest country on a major route for refugees and migrants heading north on their way to Austria and then Germany.
About 180,000 people, many fleeing war in Syria and Afghanistan, have entered the Alpine state since mid October, when Hungary fenced off its border with Croatia and pushed the migrant route towards it western neighbour.
Prime Minister Miro Cerar said on Tuesday the border would remain open, but the fence would help control the flow of people.
He said his country would not have the resources to shelter large numbers of migrants over the harsh winter if Austria shut its border, creating a bottleneck.
About 175 policemen from other EU states have come to Slovenia to bolster the local force, with another 100 expected in the next two weeks.
Slovenia prepares to erect fence to control migrants
11 November 2015
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Trucks carrying wire fencing arrived in the Slovenian village of Veliki Obrez close to the border with Croatia early on Wednesday, a day after the government said it would start erecting barriers to control the flow of migrants.
