It's now thought that at least 51 bodies were found in the hold of a boat off the coast of Libya during a rescue operation which saved around 430 others.
A Swedish ship working with the European Union's border control agency Frontex discovered the grim cargo when going to the aid of a boat in difficulty.
It's not the first time migrants have been packed below deck - most of those who died were women and children.
Save the Children spokesperson Giovanna Di Benedetto said that according to accounts by teenagers on board they confirmed they had been traveling in the hold with the mothers and children, and they were forced to pay to be allowed on deck to get some fresh air even for a few minutes.
Yesterday's rescue operation was one of 10 such missions which have picked up around 3,000 migrants mainly from Africa and the Middle East - according to the Italian coastguard.
Smugglers based in Libya are thought to be taking advantage of calmer seas to send packed vessels towards Europe.
More than 100,000 migrants have reached Italy so far this year. But at least 2,300 are believed to have died while trying to make the crossing.
Source: Euronews
