Five people have been injured in clashes between Syrian and Afghan migrants at an overcrowded detention camp on the Greek island of Chios, authorities said.

The clashes early on Friday are the latest in a series of violent incidents at shelters and gathering points across Greece, where more than 50,000 migrants and refugees are stranded following Balkan border closures supported by the European Union.

Greece has been detaining migrants who arrived after March 20 and will begin deporting them back to Turkey next week, under an EU-Turkey agreement on migration.

The deportations will start with migrants whose asylum claims are considered inadmissible - a group likely to include citizens of Afghanistan.