Macedonian police have fired tear gas to disperse thousands of migrants trying to enter from Greece.
It comes a day after Macedonia declared a state of emergency in two border regions to cope with an influx of migrants, many from the Middle East.
Large numbers spent the night stuck on Macedonia’s southern frontier, and tried to charge police in the morning.
The Balkan nation has become a major transit point for migrants trying to reach northern EU members.
Some 44,000 people have reportedly travelled through Macedonia in the past two months.
At least eight people were injured in the clashes at the border with Greece, AP reported.
In recent weeks there have been chaotic scenes at Gevgelija station, with migrants trying to clamber on board packed trains bound north.
As well as Gevgelija, Macedonia also declared a state of emergency in northern Kumanovo, where migrants attempt to travel on to Serbia.
Greece itself has seen almost 160,000 people landing on its shores since January, the UN estimates, with 50,000 arriving in the past month alone.
There were fears that by effectively shutting off its borders, Macedonia would create a backlog of migrants at its frontiers.
Those trying to reach northern and western Europe come from the Middle East, Africa and Asia, but many arriving in Macedonia are escaping the conflict in Syria.