It began with blips on a radar screen, 12 miles off the Libyan coast. As the rescuers approached, they found overloaded wooden vessels and rafts that evoked scenes of the slave trade.
Aris Messinis, an Agence France-Presse photographer aboard the rescue boat Astral, said it was like nothing he had ever seen.
The passengers — from Eritrea, Ethiopia, Somalia, Nigeria and other sub-Saharan countries — were found by the Astral on Tuesday, part of a wave of more than 11,000 rescued in the Mediterranean by aid groups and the Italian Coast Guard this week.
Migrants aboard a large wooden boat, which may have held 1,000 people — roughly five times its capacity — waited frantically for help. Some jumped into the water.