Thirty people are missing and 17 were rescued in the central Mediterranean on Sunday after the boat in which they were travelling from Libya capsized in bad weather, Italy's coast guard said.
Rescue operations were ongoing, supported by merchant ships and aerial support by the EU's border agency Frontex, while two further merchant vessels were en route to the area, the coast guard said in a statement.
Earlier on Sunday, the Mediterranea Saving Humans charity had tweeted that according to several sources, the vessel, travelling in the direction of Italy, had capsized about 110 miles north-west of Benghazi.
Alarm Phone, another charity which picks up calls from migrant vessels in distress, said on Twitter it had first alerted authorities on Saturday, emphasising the boat, which was carrying 47 people, needed immediate rescue.
After an initial rescue attempt by a merchant ship failed due to bad weather, Libyan authorities asked Rome for help given that they lacked the means to carry out the rescue, the coast guard said in the statement.
Rome then requested merchant ships in the area to join the rescue efforts, noting that the capsize occurred outside Italy's Search and Rescue area (SAR).
However, the migrant vessel turned over during an attempt to transfer the people on to the "FROLAND" merchant ship on Sunday morning, it said.
Mediterranea's head of mission Luca Casarini told Reuters that four merchant vessels were still in the area.
Italy's capabilities to rescue migrants at sea have come under scrutiny following a Feb. 26 shipwreck near the southern region of Calabria, in which at least 79 died.
On Saturday the coastguard said that more than 1,300 migrants had been rescued in three separate operations off the southern tip of Italy, with a further 200 saved off Sicily.