Austria is bracing for an influx of 10,000 migrants as Europe's increasingly divided countries step up efforts to push the wave of desperate humanity on to their neighbours.
In the latest chapter in the EU's escalating refugee crisis, Croatia, Hungary and Slovenia tussled over how to cope with the massive inflow of people passing through on their way to new lives in northern and western Europe.
The European Union, meanwhile, sketched out plans to boost aid to encourage Syrians in Turkey to stay put rather than join the exodus.
Hungary's right-wing government, which has faced international criticism over violent clashes with migrants and a hastily erected fence along its frontier with Serbia, has vowed to "defend its borders" against the flood of new arrivals, most of whom are from the Middle East and Africa.
But in a shift in tactics late on Friday, Hungarian authorities began transporting thousands of migrants straight to the border with Austria, an apparent bid to move them through and out of their territory as quickly as possible.
Austrian police said Hungary had bussed at least 6700 people to the border, with a total of 10,000 arrivals expected in the Burgenland border region by the end of Saturday.
There was no let-up in the stream of people making the gruelling journey across the Balkans into western Europe, with Croatia saying 20,700 had entered the country since Wednesday.
Croatia, which initially said it would allow migrants to pass through freely, announced it was swamped on Friday and began transporting hundreds to the Hungarian border - sparking a furious reaction from Budapest.
Migrants were being transported on Friday to two border crossings with Hungary and two with Slovenia, Interior Minister Ranko Ostojic said.
Both countries belong to Europe's borderless Schengen zone.
In a new hurdle aimed at stemming the influx, Hungary said it had completed a 41-kilometre barbed-wire barrier along part of its frontier with Croatia.
It "was finished overnight on Friday," defence spokesman Attila Kovacs told AFP in Budapest.
The remaining 330km of the border runs roughly along the Drava river, which is difficult to cross.
The new barrier adds to a barbed-wire fence that Hungary completed along its frontier with Serbia earlier this week, backed with laws threatening illegal migrants with jail, which forced the migrant flow towards neighbouring Croatia.
The first migrants to have taken this diverted new route - through Croatia and Slovenia - arrived in Austria on Saturday, from where many hope to travel on to elsewhere in the European Union.
About 150 people crossed the border, local police said, and were being looked after by the Red Cross in the town of Styria.