About 200 people were left homeless when fire tore through a refugee camp on the Greek island of Samos.
Tensions between Arabic-speaking and African migrants started on Sunday and the dispute intensified into stone-throwing and setting fires, Greek officials said.
Riot squads were sent to the overcrowded camp on Samos where nearly 7,000 people are staying with facilities built to handle fewer than 650. Seven people were arrested.
The Greek government had planned to relocate to the mainland more than 2,300 asylum seekers from island camps, including many elderly and ailing people, but the operation has been delayed owing to fears of coronavirus contagion.
No coronavirus case has been officially reported in camps on the islands of Lesbos, Chios, Samos, Leros and Kos. But there have been outbreaks in two camps and a migrant hotel on the mainland.
Another fire in the migrant camp on Chios earlier this month destroyed the facilities of the European asylum service, a camp canteen, warehouse tents and many housing containers in a riot started after a 47-year-old Iraqi woman died there. Residents attributed her death to coronavirus. Officials denied this was true.
A blaze also severely damaged an education centre on Lesbos last month and another camp on the island was damaged by fire a few days earlier as tensions increased over a surge in migrants to Lesbos.