Reuters reports that rescuers scoured the seas off Greece on Thursday following a shipwreck that killed at least 78 migrants, as hopes of survivors dwindled and fears grew that hundreds more, including children, may have drowned inside the crowded vessel’s hold.

Reports suggested between 400 and 750 people had packed the 20 to 30-meter-long fishing boat that capsized and sank early on Wednesday morning in deep waters about 50 miles (80 km) from the southern coastal town of Pylos. Greek authorities said 104 survivors had been brought ashore.

A shipping ministry official said nine Egyptians were arrested over the shipwreck. Greek TV Skai reported that, according to witnesses, the vessel departed from Egypt and stopped at the Libyan port of Tobruk before setting sail for Italy.

“The shipwreck off Pylos marks one of the largest sea tragedies in the Mediterranean in recent memory,” Maria Clara, the UNHCR representative in Greece, told Reuters.

9 arrested after deadly migrant shipwreck near Greece leaves at least 78 dead

Thanks to Alaric Bond for contributing to this post.