ROME (CNN) -- Rescuers are searching for dozens of people feared missing at sea when a boat carrying as many as 100 migrants ran into trouble overnight, Italian officials said Friday.
At least 56 people have been rescued so far, some from the sea and others from the small island of Lampione, said Filippo Marini, a coast guard commander. They appeared to be mainly Tunisian, he said.
It was unclear what kind of trouble the boat ran into.
Survivors picked up during the night reported that there were about 100 people on the ship, said Laura Boldrini, head of the U.N. refugee agency in Italy.
Coast guard officials located the migrants soon after midnight following a distress call from the ship, Marini said.
Italian police boats and three NATO ships were involved in the search overnight, which was made difficult because of the dark, he said.
Two helicopters and a fixed wing aircraft were also deployed for the rescue operation, Marini said.
The migrants, who've been rescued so far, have been taken to the tiny Italian island of Lampedusa, where their details will be taken, he said.
It's not yet clear where the boat set out from, he added.
Lampedusa, the closest Italian island to Africa, has become a destination for tens of thousands of refugees seeking to enter European Union countries.