Rome (CNN) -- Rescuers searched 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 are believed to be Tunisians, he said.
At least one body has been found, said Capt. Davide Miserandino of Italy's finance police, which is helping in the search.
Survivors picked up during the night reported that there were about 100 people on board, said Laura Boldrini, head of the U.N. refugee agency in Italy.
It's unclear exactly what happened to the boat.
The vessel started taking on water and presumably sank when it was about seven nautical miles west of the island of Lampedusa, near Lampione, Miserandino said.
A pregnant woman was among those rescued.
Some of the rescued passengers were suffering symptoms of hypothermia but are now doing better, he said.
Coast guard officials found the migrants soon after midnight, following a distress call from the boat, Marini said.
Three NATO ships joined Italian coast guard and police vessels in the search overnight, which was made more 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 Lampedusa, where information about them will be taken, he said.
Miserandino said the migrants had probably left from Tunisia.
Lampedusa, the closest Italian island to Africa, has become a destination for tens of thousands of refugees seeking to enter European Union countries.
Boats carrying migrants often are in peril at sea.
Amnesty International reported at least 1,500 deaths last year of people attempting to cross the Mediterranean Sea.
The human rights monitoring group said some of the deaths could have been prevented.
"The desire of some European countries to prevent irregular migration (people who do not have permission to live and work in these countries) has undermined safe and timely rescue at sea," Amnesty International said.
At least 61 people died Thursday when a boat believed to be carrying illegal migrants sank off the coast of Turkey. They were believed to be Syrians and Palestinians.