Riot police have fired tear gas and stun grenades as thousands of people try to enter Macedonia from Greece.
There were several attempts to charge officers by angry people among a crowd of 3,000 from the Middle East, Africa and Asia.
They had spent the night in the open in a no man's land between the two countries after Macedonia sealed its southern border to migrants and refugees.
At least eight people were injured in the confrontation earlier and one youngster was seen bleeding.
A state of emergency has been declared by Macedonia because of the number of people wanting to head north to Europe.
Coils of razor wire have also been spread over rail tracks used to cross on foot to Macedonia from Greece, which has seen a surge in the number of people trying to reach its islands from Turkey.
Authorities in Greece, particularly on the tourist hotspot islands, have been overwhelmed by the influx - some 160,000 have arrived in Greece so far this year.
Others have walked to Bulgaria from Turkey before making their way through Macedonia or Serbia before heading north to the EU.
Some 39,000 migrants, mostly Syrians, have been registered as passing through Macedonia in the past month - twice as many as the previous month.
