While at least 78 people are known to have perished, reports indicate that as many as 750 people—including as many as 100 children—may have been on board the vessel.
One hundred and four survivors—all of them men—were rescued after the boat sank about 50 miles from the southern coastal town of Pylos. It is feared that women and children were being kept below deck, and that they perished when the vessel capsized and sank on 14 June.
The area of international waters is one of the deepest in the Mediterranean.
Survivors were brought to the port city of Kalamata by the coastguard, where many are being treated for conditions including hypothermia and dehydration.
The boat is thought to have set off from the Libyan port of Tobruk and was heading to Italy.
Greek authorities said most of the migrants were from Egypt, Syria, and Pakistan. The Greek government has declared three days of national mourning.
Archbishop Ieronymos of Athens, primate of the Church of Greece, expressed condolences.
“No words can express the deepest pain I feel today as a human being and as a clergyman for the untimely and tragic loss of dozens of our fellow human beings in the shipwreck in international waters off Pylos,” he said.
“In the midst of death and trauma caused by this terrible event, let us bring our intercessions together, praying that the God of Life will comfort the ones who lost their loved ones and give strength to those involved in the actions of solidarity with the victims,” said Rev. Prof. Dr Jerry Pillay, general secretary of the World Council of Churches.
“We convey our prayers to the victims and their families, as well as to the churches in Greece mobilizing their networks to help their sisters and brothers,” added Pillay.