Four women and a child drowned in the Aegean Sea when the boat they were travelling on capsized in rough waters and stormy weather, Greek television network Skai reported Saturday.
European border agency Frontex and the Greek coastguard responded to the overnight incident near the Greek island of Samos with the deployment of four rescue boats.
Five people survived the incident after treading water for three hours until the boats arrived, according to the report.
It was unclear how many people were on the boat in total, the report said. The vessel had departed a short time earlier from Turkey.
A helicopter was reported to have circled the waters in search of survivors.
The deaths are the first reported in the Aegean Sea in several weeks.
Greece's refugee crisis committee said this week that it had charted a sharp drop in the number of migrants arriving in Greece from Turkey. In March, 900 migrants were reaching Greece on average per day.
The drop follows a deal struck between the European Union and Ankara to return the majority of new arrivals to Turkey in a bid to prevent irregular migration to Greece via perilous sea routes.
The committee said that 120 people had arrived at the Greek islands over the course of Friday and Saturday, with Lesbos receiving the majority. The EU-Turkey agreement came into effect on Monday and subsequent arrivals have little chance of being allowed to stay in Greece as a result.