More than 300 people likely died in a major shipwreck off the Greek island of Crete last week, the International Organization for Migration (IOM) said Tuesday.
Several survivors have reported that the vessel was carrying 650 people when it sank on Friday en route from Egypt to Italy, the aid and advocacy group said in Geneva.
In addition to nearly a dozen corpses that were recovered last week, 320 people remain missing and are presumed to have drowned, spokesman Joel Millman reported.
One 3-year-old girl survived because her father entrusted her to another migrant, asking him to look for her relatives in Egypt.
The girl's father, mother and two brothers died, the migrant told IOM staff after he was rescued along with other survivors.
Including this latest accident, 2,809 have perished in the Mediterranean this year as they tried to reach Southern Europe in search of refugee protection or a better livelihood.
"Fatalities on the Mediterranean Sea in 2016 are nearly 1,000 ahead of last year's mid-year total," Millman said.
He said there was a sharp rise in children trying to cross the sea to join family members who are already in Europe.
"Visa processes take a long time, so there is a strong urge to give your children into the hands of smugglers," he said.
The biggest national groups arriving in Italy are from Eritrea, Nigeria and Gambia, while those who have reached Greece this year were mainly from Syria, Afghanistan or Iraq.
Meanwhile in Greece, the main European gateway for migrants last year, the authorities revised the number of people registered on its soil upwards by nearly 10 per cent.
The body in charge of migrants attributed the rise to the first-time inclusion of migrants staying in UN-run camps.
With that, the number of registered refugees and migrants rose to 57,458, some 7,500 of whom are sheltered in the so-called hotspots on Aegean islands.
They have been stranded in Greece since neighbouring Macedonia followed the example of other countries further north by sealing its border to migrants in March.
That same month, the European Union and Ankara agreed to send new arrivals back to Turkey. In return, the bloc has said it will resettle Syrian refugees directly from Turkey, but there has been slow progress on this side of the deal in practice.
The number of arrivals from Turkey to Greek islands has declined dramatically since, from highs of thousands each day to one or two dozen.
Over 1 million migrants and refugees made it to Europe's shores over the course of 2015, followed by more than 206,000 arrivals since the beginning of this year, according to a UN tally.