Nine people have been rescued from the boat, which sank off the southern tip of Evia, Greek coast guard spokesman Nikos Kokkalas told state broadcaster ERT.
According to the migrants' accounts, about 68 people were on the boat, Kokkalas said, according to Reuters.
A coast guard vessel, a helicopter, and two boats sailing nearby are taking part in the rescue operation under gale-force winds, the coast guard said in a statement.
MP/PR