Austria is building a fence on a small stretch of its border with Slovenia, the latest country to erect a barrier in efforts to manage the flow of migrants.

A 3.7 kilometre chain-link fence will be built at the Spielfeld crossing that has been the main entry for migrants from Slovenia over the past weeks, a police official said.

Interior Minister Johanna Mikl-Leitner said earlier on Friday that Austria had decided not to build a 25-kilometre fence along a stretch of its border with its southern neighbour for now after Slovenian authorities asked it not to.

Ms Mikl-Leitner said Austria reserves the option of building the longer barrier if Slovenian border measures prove inadequate in ensuring that the migrant flow into Austria is orderly.

Meanwhile, an international migration monitoring and response agency said the influx of migrants into Europe has slowed down.

The International Organisation for Migration said around 31,000 refugees or other migrants had entered Greece over the previous week, a 38% drop from a week earlier.

Spokesman Leonard Doyle cited concerns about the weather and growing awareness of the dangers of crossing the Aegean "in a small rubber dinghy".

Arrivals fell by 25 to 30% in Macedonia, Serbia, Croatia and Slovenia, along the route used to reach places like Germany and Sweden.

More than 810,000 people have crossed the Mediterranean this year, and over 200,000 in October alone. Four out of five this year have crossed from Turkey to Greece.