Overnight clashes between Syrian and Afghan refugees left two people seriously injured with police using tear gas and stun grenades to restore order.
The entire group entered Greece after the March 20 launch of the EU-Turkey agreement, which calls for them to be detained in a hotspot until a decision is made concerning their fate.
Similar riots had earlier flared up at Piraeus harbor with hundreds of migrants fighting and pelting one another with stones. Eight people were later hospitalized.
Tensions inside the refugee camps on Chios Island had been heating up since the Balkan countries refused to let the refugees pass through their territory effectively stranding thousands of refugees in Greece.