Greece's coast guard says a search and rescue operation is underway off the coast of the eastern Aegean island of Lesbos after a boat carrying dozens of migrants capsized.

The coast guard said Tuesday 57 people have been rescued, while seven people, including two children, were pulled from the water unconscious.

There is no clear indication from the survivors as to exactly how many people were on board, the coast guard said. Vessels from the coast guard, a volunteer rescue organization, Europe's border patrol agency Frontex and a helicopter are searching the area.

Although the number of people heading to the Greek islands from the nearby Turkish coast has decreased since the height of the refugee crisis in 2015, hundreds continue to arrive each week.