The bodies of at least eight people, including six children, have been recovered after a migrant boat sank off the Greek island of Samos, the coastguard has said.
Around 40 people were rescued by authorities during an operation in the Aegean Sea involving aircraft and vessels, authorities said.
Strong winds have been complicating rescue efforts.
An official said a non-governmental organisation alerted authorities, and that it was believed about 50 people were on board the vessel.
Greece's migration minister, Nikos Panagiotopoulos, said the incident "fills us with sadness and anger", while also pledging to crack down on people-smugglers.
More than 50,000 migrants have arrived in Greece by boat so far this year, making it the second most used European migrant route - behind only Italy.
Migrant arrivals had been steadily declining since August 2023, but increased again since summer, according to data from United Nations refugee agency, UNHCR.
About 160,000 migrants have arrived in Europe by sea this year, agency figures show, while 2,000 people were dead or missing.
Around 23 percent of arrivals were children.