ROME — The crew of an Italian Navy ship that responded to a distress call on Saturday morning from a boat carrying hundreds of migrants discovered the bodies of more than 20 people piled on top of one another in the boat’s hold, Italian officials said. It was another ghastly reminder of the perils faced by migrants crossing the Mediterranean in overcrowded and unsafe vessels.

By Saturday afternoon, the crew of the navy patrol ship Cigala Fulgosi had saved 312 people, including 45 women and three children, from the nearly 50-foot-long boat and had recovered eight bodies from the hold. But many more bodies remained below, Cmdr. Massimo Tozzi said in an interview from the ship.

“The bodies are massed on top of each other,” Commander Tozzi said. “It’s still difficult to know how many there are. Maybe 20, maybe more.”

The migrants were apparently overcome by fuel fumes, and the bodies were immersed in water and fuel. “It seems like carbon monoxide poisoning,” he said. “At first glance, there were no visible wounds” or signs of drowning.