The Greek coast guard says it has rescued 24 people and recovered the body of one man from the southern part of the Aegean island of Lesbos.
A search and rescue operation has been launched for potentially missing people.
The 25, believed to be migrants who had arrived from nearby Turkey, were located on an inaccessible part of the island’s coast on Tuesday and were transported from the area by a coast guard vessel.
A helicopter and several coast guard vessels were searching the area following reports from the migrants that there could be a further three people missing.
Officials said it was not immediately clear how the group arrived or what had happened to their boat.
The short but often perilous journey from the Turkish coast to nearby Greek islands has been one of the most popular routes into the European Union for people fleeing conflict and poverty in the Middle East, Africa and Asia.
Many make the journey in unseaworthy and overcrowded boats.
A 2016 deal between the EU and Ankara stipulates that new arrivals be held on the islands pending deportation back to Turkey unless they successfully apply for asylum in Greece.
The deal has led to massively overcrowded refugee camps on the Greek islands.