PALERMO, Italy—On a mid-September afternoon the sun beat down on cruise ships and freighters moored in Palermo's port. In front of white canvas tents—impromptu clinics erected earlier in the day—masked medics from the Italian Red Cross, police officers, fire fighters, employees of the Dipartamento della Protezione Civile (Civil Protection Department), priests, translators, officials with the local prefecture, and journalists waited expectantly. Ambulances and water trucks stood nearby.

New arrivals—442 of them, most having embarked on a perilous Mediterranean crossing from Libya—were due any moment at the port in Sicily. They were hours late: Heavy seas had impeded their transfer from the commercial ship that had rescued them at sea to the vessels of the Italian Coast Guard.

A coast guard patrol boat