Two barracks at the Samos camp were torched in the unrest yesterday, which was apparently sparked by a brawl between migrants. Their nationalities were not immediately given.
Police reinforcements were sent to the scene and six people were taken to hospital "as a precaution", a police source told AFP.
The crowded camp houses around a thousand migrants and refugees, including many families with children.
"We're surprised because the atmosphere here is usually quite calm," said Samos Dimitris Vouros, who works for the Metadrasi charity active at the camp.
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Over a dozen migrants were injured and hundreds had to be evacuated as rival groups of Afghans and Pakistanis went at each other with clubs and stones, an AFP correspondent at the scene said.
The spokesman of the UN refugee agency's mission to the island, Boris Cheshirkov, said a number of tents were set alight during the incident.
Three of the wounded -- two Pakistanis and an Afghan -- were hospitalised, two of them with head injuries.
Nearly a thousand of them left after the clashes, seeking refuge in the surrounding fields and in another migrant camp, the AFP reporter said.
Some 50,000 migrants are currently stranded in Greece after Balkan states began shutting their borders in February to stem an exodus of thousands to northern Europe.
Most are staying in overcrowded camps whose poor living conditions have frequently been criticised by rights groups.