In western Croatia, up to 2,000 more spent the night on a train stranded near the border with fellow EU member Slovenia, which was refusing entry.
With Hungary closing its border with Croatia to migrants at midnight on Friday, the unrelenting flow has been diverted to Slovenia en route to Austria and Germany, the favoured destination for most migrants, many of them refugees from the Syrian war.
But Slovenia has imposed a daily limit of around 2,500, saying it will only take in as many as can exit into Austria.
Slovenia said Austria was accepting a maximum of 1,500, far fewer than were previously entering from Hungary, though the Austrian interior ministry said it could not confirm this.
Upwards of 5,000 are flowing across Balkan border daily, from Greece where they arrive by boat and dinghy from Turkey, into Macedonia and Serbia, both poor former Yugoslav republics with barely the capacity to cope.
A Reuters reporter on the Serbian side of the border with Croatia said there was no apparent police presence to help maintain order. Cold and tired, migrants chanted "Open the gate, open the gate!"
The arrival of a projected 700,000 migrants this year to Europe`s shores, fleeing war and poverty in the Middle East, Africa and Asia by boat and dinghy across the Mediterranean and Aegean, has exposed deep and often ugly divisions in the EU.
Hungary`s right-wing government says the mainly Muslim migrants pose a threat to Europe`s prosperity, security and "Christian values", and has sealed its borders with Serbia and Croatia with a steel fence and stringent new laws that rights groups say deny refugees their right to seek protection.
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