They were the latest of nearly 3,500 deaths at sea this year among people making desperate bids to flee war and poverty and to reach Europe, according to UN figures.
The coastguard recovered six bodies from the water, while divers found the remains of two others trapped in the sunken boat.
Seven survivors from the same vessel said up to five other migrants were still missing. Rescue efforts were under way today morning, the coastguard said.
The boat, which came from nearby Turkey and which capsized overnight, was spotted by the crew of a Finnish ship participating in operations by Frontex, the EU's border security agency.
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More than 800,000 migrants, mostly fleeing war and persecution in Syria, Iraq and Afghanistan, have crossed the Mediterranean this year to reach Europe.
The vast majority have reached Greek shores, from where they travel up to the Balkans and on towards countries like Germany and Sweden where they apply for asylum.
Greece's Prime Minister Alexis Tsipras was set to visit Turkey starting today to urge authorities to impose stricter controls on the trafficking of migrants into Europe.