About 400 migrants died in an attempt to reach Italy from Libya when their boat capsized, survivors said on Tuesday, the latest tragedy in the Mediterranean where the death toll from shipwrecks has surged this year.

The boat, carrying about 550 migrants in total, flipped about 24 hours after leaving the Libyan coast, according to some of the 150 survivors who were rescued and brought to a southern Italian port on Tuesday morning, Save the Children reported.

Before this incident there had already been more than 500 deaths of migrants crossing the Mediterranean from Africa this year, up sharply from 47 in the same period of 2014, said the Geneva-based International Organization for Migration (IOM).