Hundreds of migrants attempting the perilous journey across the Mediterranean are feared to have drowned after their overcrowded fishing boat capsized off Libya.
Italy's coastguard on Wednesday said the boat had run into difficulty some 15 nautical miles off Libya and sent out a distress call.
The call was picked up by the coastguard in Catania in Sicily.
Two vessels - the Medecins Sans Frontieres ship Dignity One and the Irish patrol vessel Le Niamh - were immediately dispatched to the scene, but the boat capsized after the migrants all rushed to one side in anticipation of being rescued, the coast guard said.
Nawal Soufi, an Arabic-speaking Italian based in Sicily who is often contacted by migrants in distress, told AFP she had had a call earlier on Wednesday about a boat in trouble with some 600 people on board.
"It is probably the same boat," coastguard spokesman Filippo Marini said, raising fears that hundreds of people may have disappeared below the waves.
Three other ships have been sent to the area to search for survivors.
More than 2000 people have died trying to cross the Mediterranean to Europe this year according to the International Organisation for Migration.