A search-and-rescue operation was underway early Thursday after a boat carrying alleged undocumented immigrants sent a distress call off the southeastern Aegean island of Astypalaia.

Early reports said the boat was carrying 83 people.

Four coast guard vessels, one Hellenic Navy frigate and two cargo ships have reportedly arrived on the scene.

Greece is a major gateway for immigrants trying to make their way illegally from Africa and the Middle East into the European Union.