Greek authorities mounted a search and rescue operation to save about 100 migrants whose vessel sank after hitting a rocky area in stormy waters near the island of Kythira on Wednesday, the coastguard said.
"Their vessel smashed into a rocky area and sank," a coastguard official said. "One coastguard vessel, joined by a Greek navy helicopter are rushing to the area."
The coastguard did not have additional information on possible casualties or on the nationality of the migrants.
Kythira is an island lying opposite the southeastern tip of the Peloponnese peninsula.
Greece was the frontline of Europe's migration crisis in 2015 and 2016, when a million refugees fleeing war and poverty from Syria, Iraq and Afghanistan arrived, mainly via Turkey.
The number of migrant arrivals has fallen sharply since, but attempts to enter the country by sea through its islands continue.
(Reporting by George Georgiopoulos; Editing by Bill Berkrot)