Search and rescue operations in the Mediterranean Sea have been stepped up, but the United Nations says much more must be done to help the thousands of migrants trying to reach Europe by boat.
It's after a ship carrying up to 900 people sank off the north African coast on Saturday.
Authorities say 28 people were rescued; but many more died.
The captain and a crew member of the boat have been arrested.
UN figures say 13,500 migrants have been rescued trying to reach Europe so far this year and around 35,000 have arrived from Africa in 2015.
European leaders are meeting this week to try to work out what to do.
Each year many thousands, many of them children, attempt to cross the Mediterranean Sea to Europe, trying to escape poverty and war in their home countries.
Official figures say nearly 220,000 tried to make the journey in 2014.
The journey is very dangerous: criminal gangs organise the crossings illegally, which means there's no-one checking that conditions are safe.
People are packed very tightly into small boats, which leak and often sink.
The biggest numbers arrive in Italy and Greece, because these countries are directly across the sea from Libya in north Africa.
Even if people do make it, they may not be allowed to stay in Europe. There are rules over who can and can't stay, so many have to be sent back to their own countries.