ATHENS — A search and rescue operation was underway Thursday morning off the coast of an eastern Greek island for four migrants who were missing as a boat attempted to reach Greece from the nearby Turkish coast, authorities said.

The coast guard said authorities had received a distress call regarding a boat in trouble off the southern coast of the island of Samos, and found 18 people on board when they arrived in the area. The passengers said there had been a total of 22 people on board, and that four of them had fallen into the sea.

Two Greek coast guard patrol boats and one vessel from the European border patrol agency Frontex were participating in the search and rescue operation, as well as two helicopters.

The 18 survivors were being transported to Samos. Their nationalities weren’t immediately known.