At least 26 migrants, including 10 children, drowned late on Thursday night when their boat sank off the island of Samos, Greek Coast Guard officials said.
Rescuers managed to save nine migrants — including another two children — while the search resumed on Friday for possible survivors.
The rescue operation began on Thursday when a migrant who had been on the wooden boat that had attempted the crossing from Turkey to Greece managed to swim to the island's northern coast. He told rescuers that the boat had taken on water and foundered.
The incident raised the death toll in Aegean crossings by migra
nts to at least 80 in the past week, officials said.
More than 900,000 people fleeing Syria, Afghanistan and other war-torn or impoverished countries arrived in Greece from Turkey last year, often risking the short but dangerous sea crossing in overloaded boats.
The inflow has continued unabated through the winter months despite the cold conditions and choppy sea, with about 2,000 people landing on Greece's islands a day, according to data by the United Nations' refugee agency, UNHCR.
Few, if any, of arrivals to Greece choose to stay and seek asylum in the country, which is struggling through its worst peacetime economic crisis. Most continue their trek through Greece and the Balkans to wealthier western European countries.
On Wednesday, the European Commission warned there could be more controls over movement between Greece and other states in the free-travel Schengen zone from May unless Greece fixed "serious deficiencies" in its management of the zone's external frontier.
Several EU member states have instituted emergency controls on their borders and warned they may effectively suspend Athens from the passport-free zone.
The mayor or Lesvos, the island through which most refugees and migrants passed last year, said on Thursday such warnings were "completely unfair, completely absurd."
"More than 550,000 people passed through the island of Lesvos alone – which is but a dot on the global map – and we didn't close borders," he said. "Greece is doing whatever it can. It's doing a lot more than it can."
Philippe Leclerc, the UNHCR's acting Greece representative called on EU countries to "act together, and not individually."
"Every state … has to play its part and we count on them to show responsibility, trust and solidarity far more than they have shown today," he said during a visit to the Eleonas refugee camp in Athens, which houses mostly Afghans and Iranians.