Croatia joined the Eastern blockade of Western Europe-bound refugees, when it closed seven of its eight border crossings with Serbia "until further notice".
The move was announced by the country's Interior Ministry after 11,000 migrants crossed the border within 48 hours.
In Slovenia, police stopped a train carrying 150 refugees from arriving from Croatia. Border police said the migrants did not have the correct papers and would be sent back to Zagreb, the Croatian capital.
Earlier in the day Hungary declared success for its controversial efforts to seal its borders to migrants, as thousands of new arrivals headed into neighbouring Croatia instead.