The other ship, carrying 356 migrants, reported that it was in difficulty and was towed to Libya, according to another official with the group, Laurence Hart, who was in Tripoli, Libya’s capital.

Image A police officer in Tripoli, Libya, helped off a boat migrants who had been rescued after their boats ran into a violent storm that struck off the coast of Libya. Credit... Agence France-Presse — Getty Images

Mr. Chauzy said his organization was “still without news of two other boats that were caught out in the storm.” It was not clear whether they were fishing boats or smugglers’ boats or what happened to the people on board.

Every year, tens of thousands of poverty-stricken people try to cross from Libya to Italy  a favored destination for migrants seeking to circumvent European immigration restrictions, often via a small Italian island called Lampedusa between the coasts of North Africa and Sicily.

The crossing spans a divide between the poverty of the developing world and the perceived riches of lands to the north. Once they have landed in the European Union, migrants may travel with ease among the 15 of the union’s 27 member nations that are grouped by the so-called Schengen agreement, which permits travelers to cross borders without identity papers.

Even as European economies shrink because of the global recession, the number of would-be migrants is unlikely to ease since their own homelands are also blighted by the economic slump.