Greece's largest migrant camp was partly evacuated early Wednesday after a major blaze broke out at the overcrowded and unsanitary home to nearly 13,000 asylum seekers.

Nearly the entire Moria camp on the island of Lesbos was on fire, including in an olive grove outside the walls of the main compound where many asylum seekers sleep in tents, an AFP photographer at the scene reported. 

Asylum seekers were fleeing on foot towards the port town of Mytilene but were blocked by police vehicles, the photographer added.

Firefighters said earlier there were "scattered fires" around and inside the camp, which has a nominal capacity for fewer than 2,800 people.

Stand by Me Lesvos, a refugee support group, said on Twitter it had received reports that Greek locals on the island had blocked fleeing asylum seekers from heading into a nearby village. 

"The whole camp is on fire. Everything is burning. People are escaping. Their homes in Moria are gone," the organisation said.

Greek news agency ANA said the fires had started after a revolt by asylum seekers who were to be placed in isolation after testing positive for coronavirus or coming into close contact with an infected patient. 

The camp has seen a spike in coronavirus infections since reporting its first case last Wednesday, with 35 confirmed cases so far.