“The number of passengers was 750,” said the governor of the Peloponnese, Panagiotis Nikas.
So far 104 people have been rescued.
The fishing boat had set sail from Tobruk, Libya, and was headed for Italy, according to initial information gathered by the coast guard.
European Council President Michel tweeted: “Migrant dossier at EU summit, tragedy is a reminder, stop the business of traffickers”.
The Italian coast guard said Thursday they had been contacted Tuesday by the boat and had informed their Greek counterparts about its approach to Greece after it wildly veered off course.
The Italian Maritime Rescue Coordination Centre received an e-mail on Tuesday morning indicating a vessel in distress with around 750 migrants on board, the Italian authorities said.
No location was given in the report, only the number of a satellite phone on board.
The Rome Coast Guard Operations Centre, upon receiving the communication, contacted the number while initiating procedures to locate the phone.
Having ascertained that the vessel was in the area of responsibility for search and rescue (SAR) at sea in Greece, 60 nautical miles from the Greek coast and 260 nautical miles from the Italian coast, the Centre immediately contacted the Greek Coast Guard, providing it with all the information it needed for rescue operations, said the Italian Coast Guard.
There are still hundreds missing including around 100 children who were in the hold of the trawler, which capsized after a Greek coast guard ship started dragging it into safety using a rope.
“Three survivors told us that the accident happened when the Greek coast guard attached a rope to the trawler and was trying to tug it along,” Kriton Arseni, a representative of the movement founded by former finance minister Yannis Varoufakis, told ANSA.
“There are scant hopes of finding survivors,” said the Greek coastguard.
ANSA