The bodies of 25 people, including 10 children, have been discovered off the Greek island of Samos after their boat capsized, the Greek coastguard said.
Ten people from a dinghy carrying between 45 people were still listed as missing following the latest tragedy involving overladen migrant boats crossing the Aegean Sea from Turkey to Greece.
Ten people were rescued unharmed.
Authorities initially said they had found 12 bodies but the number rose quickly as rescuers combed the waters for the missing.
There were "five boys and five girls among the victims, while 10 people were pulled from the water unharmed, but in a state of shock," a coastguard spokeswoman said.
The alert was raised by one of the survivors, who managed to swim to shore.
Greek ships and two vessels from the European border agency Frontex took part in the rescue operation.
There was no information yet on the migrants' country of origin.
Despite wintry conditions, thousands of people fleeing war and poverty in the Middle East, Asia and Africa continue to make the treacherous sea journey to Europe, many paying with their lives.
Last week, 44 people drowned in a single day when three migrant boats ran into trouble in Greek waters.
Yesterday rescuers found the bodies of seven drowned people, including two children, after their boat sank off the Greek island of Kos.
The latest tragedy comes as swamped Greek authorities are under pressure from their European counterparts to staunch the migrant flow.
The European Commission has hit out at overwhelmed Greek authorities, saying in a report published yesterday that Athens had "seriously neglected" its duty to protect the bloc's frontiers.
The UN says more than 46,000 people have arrived in Greece so far this year, with 200 people dying during the voyage.
Last year, Greece received over 850,000 arrivals.