84 migrants went missing when their expansive small boat sank off the Libyan coast, the international organisation for Migration says.
The small boat was found taking on the water in rough seas when the Italian coast guard received a satellite telephone.
It diverted the merchant ship to rescue 26 survivors and convey them to Italy.
A voice for the coastguard said that similar boats utilized by individuals smugglers might hold 100-120 individuals, and were typically full.
Rough seas and waves topping two metres (seven feet) hampered rescue efforts.
No details of the nationalities of the migrants, who were delivered to the island of Lampedusa, were instantly obtainable.
Around 27,000 refugees and different migrants have reached Italy by boat so far this year, most of them popping out from Libya.
Officials suppose the amount trying the illegitimate crossing to rise because countries within the Balkans have shut their land borders.
Over 800 migrants are feared to have submerged in the southern Mediterranean this year to date.