Greek police on Monday fired tear gas at a group of angry migrants in a flashpoint border camp as they stoned a police van believed to have run over one of their own.
TV footage showed young migrants smashing the van's windshield with stones, with some in the crowd trying to restrain them.
According to a local police source, riot police intervened and quickly dispersed them in the latest incident of violence at Idomeni camp on the border between Greece and the Former Yugoslav Republic of Macedonia (FYROM).
The protest erupted after the Syrian Kurd was rushed to hospital from the overcrowded camp where more than 10,000 people have been stranded for weeks since the Balkans states shut their borders.
A Greek government source confirmed there had been a "serious accident" involving a Syrian Kurd aged around 40, who suffered cranial injuries, but declined to comment further.
The man was taken to hospital in the nearby town of Kilkis.
It was not immediately clear how he had been hurt inside the teeming camp where vehicles are forced to move at low speeds.
Greek media said he had fallen from scaffolding.
Thousands of migrants and refugees are stuck at the squalid, makeshift camp after their route to northern Europe was blocked when a succession of Balkan states shut their borders in a bid to halt the huge influx of people.
Many are refugees from the wars in Syria and Iraq.
Greek authorities have sought to clear the camp without resorting to violence but most of the migrants have refused to relocate to other facilities further inland, hoping that the borders might reopen.
A similar situation has emerged at the main Greek port of Piraeus where there are over 3,700 people. Another 400 were persuaded on Monday to move from the port to a newly-constructed camp at the nearby industrial zone of Skaramangas.
After enduring a winter of freezing rain and mud, sleeping in tents and queueing for hours for food, many are desperate for a way out.