7 May 2015 Last updated at 11:57 BST
Brig Martin Xuereb, director of Migrant Offshore Aid Station, described the operation to BBC Radio 5 live on 4 May.
Produced by Mohamed Madi
Photos provided by MOAS
The director of a non-governmental organisation that rescued a migrant boat in the Mediterranean says the 369 people on board were overcrowded like "a pack of sardines".