Greece's coast guard says eight people are missing after a wooden boat carrying migrants or refugees attempting to reach the eastern Aegean island of Lesbos sank after colliding with a patrol boat during a rescue operation.

The coast guard says 31 people on board were rescued, and the survivors reported eight people were missing. Thursday's incident occurred half a nautical mile north of Lesbos, the island that has been the entry point of the majority of those making the journey from the nearby Turkish coast.

Hundreds of thousands of people fleeing war or poverty have made the trip from Turkey to Greece so far this year. The vast majority head north to more prosperous European Union countries, and the sharp increase arrivals has triggered an EU crisis.