ROME — More than 4,000 would-be refugees were rescued at sea Thursday in one of the busiest days of the Mediterranean migrant crisis, and at least 20 died trying to reach Europe as Libyan-based smugglers took advantage of calmer seas to send desperate migrants north.
The death toll was likely to grow far higher, however, as the Libyan coast guard also reported two overturned boats between the coastal cities of Sabratha and Zwara. Only four bodies were found, raising fears that the rest of those on board had perished.
Overall, the Italian coast guard said it had coordinated 22 separate rescue operations Thursday that saved more than 4,000 lives.
"That probably is a record," said coast guard spokesman Cmdr. Cosimo Nicastro, noting that previous highs have been in the range of 5,000 to 6,000 over two days.
One 5-year-old boy got special treatment: He was airlifted from his rescue vessel to the island of Lampedusa, suffering from hypothermia, Nicastro said.
At least one smugglers' boat sank off Libya's coast, and 20 bodies were spotted floating in the sea, said Navy Lt. Rino Gentile, a spokesman for the EU's Mediterranean mission. Photos tweeted by the mission showed a bright blue dinghy submerged under the weight of migrants waving their arms in hope of rescue as an EU aircraft flew overhead.
None had a life jacket.
Two Italian coast guard ships and the Spanish frigate Reina Sofia responded to the scene. Nicastro said 96 people were rescued.
Barbara Molinario, spokeswoman for the U.N. refugee agency in Italy, said favorable weather conditions in May to October often encourage migrant crossings. She said prior to the recent rescues, some 40,000 people had been rescued so far this year, compared to 47,500 over the same period in 2015.
Among those coming ashore Thursday in Sicily were the survivors of a dramatic capsizing a day earlier off Libya's coast. Footage provided by the Italian navy showed the steel-hulled smuggler ship rocked under the weight of its passengers and finally flipped, sending migrants into the water or clambering up the side.
The Italian navy vessel Bettica brought the survivors and five bodies ashore in Porto Empedocle, Sicily. Red Cross workers took at least one migrant away in a stretcher, while rescue teams in white hazmat suits carried children down the plank to shore.
In other rescues, a Libyan navy spokesman said a total of 766 migrants were rescued by the Libyan coast guard on Thursday.
Col. Ayoub Gassim said they were found in two groups: one of 550 near the western coastal city of Sabratha and the second of 216 off Zwara.
He said two other capsized boats were found empty in waters between the two cities and only four bodies were retrieved, with the rest of those aboard feared dead. He said he had no other details, including how many migrants had been aboard the boats.
Before this week's deaths, the International Organization for Migration said only 13 people had drowned in the month of May, compared with 95 last May and 330 in May 2014. It said the figures "indicate that migrant fatalities may at last be declining" thanks to beefed-up coast guard monitoring along the North African coast.
However, improved weather conditions appear to have led to an increase in the number of migrants risking the crossing.