Nearly 3000 migrants trying to reach northern Europe crossed into Slovenia from Croatia on Saturday (local time), having been forced to change their route after Hungary closed off another border with razor wire.
Slovenia's government said 2700 men, women and children had crossed by late Saturday from Croatia into its territory, where Ljubljana deployed soldiers at the border to help police with "logistics and equipment".
The first arrivals, about 600 of them, went by bus to the border crossings of Gruskovje and Petisovci. Many had already spent weeks trekking up through Greece and Macedonia before crossing Serbia to reach the Croatian border.
After registering them at border checkpoints, Slovenian authorities were to transport them to the Austrian frontier from where they could continue to Germany, the preferred destination for many.
A majority of the migrants were from Syria, Iraq and Afghanistan, UNHCR spokeswoman Caroline van Buren told AFP at the Petisovci checkpoint.
"They are fleeing from war... They are literally running for their lives," van Buren said, adding that the procedure for now was running smoothly.
"Unlike other countries, Slovenia had time to prepare... It's not perfect, but things are moving."
The Croatian government has said it will continue to ferry migrants across the country by bus and train as long as Slovenia and Germany kept their borders open.
Hungary closed its frontier with Croatia to migrants early on Saturday in a bid to block the path of streams of refugees, a month after it sealed its border with non-EU neighbour Serbia - until then the main entry point into the EU for migrants fleeing conflict and poverty.
Later on Saturday, a special train with about 1200 migrants on board arrived at the Sredisce ob Dravi crossing, guarded by more than 100 policemen, said an AFP correspondent at the scene.
Police were organising the transfer of the travellers from train carriages to 25 buses waiting to take them to registration centres before their next journey to Austria.