Hundreds of migrants have spent the night at the closed Hungary-Serbia border, with many facing the choice of finding a new route to northern Europe.
Serbian media said buses were now being redirected to Croatia, with migrants then planning to move on to Slovenia, Austria - and finally Germany.
There have also been suggestions that Romania may become a new route.
New border restrictions and a row over allocating migrants have shown bitter divisions in Europe over the crisis.
Hundreds of stranded migrants spent the night in the open or in makeshift tents close to the Serbian border with Hungary.
A day earlier, new Hungarian laws came into effect and police sealed a railway crossing point that had been used by tens of thousands of migrants.