Thousands of migrants were forced to flee to safety on Monday when their camp on the Greek island of Lesbos was badly damaged in a fire apparently set on purpose, police said.

No casualties were reported but tents at the Moria camp were "almost entirely destroyed" and containers that provide additional accommodation and health and registration services were damaged, said a police source in Athens.

Firefighters were prevented from tackling the fire early on by clashes that broke out among rival nationalities in the camp, reports said.