Three migrants died in the Mediterranean on Monday night, a German aid group said, during rescue operations in which thousands more were pulled to safety from rickety boats.
About 5,000 migrants were picked up off the Libyan coast by emergency services, Italy's navy, aid groups and private boats on Monday, and further rescues were ongoing on Tuesday, an Italian coastguard spokesman said.
German humanitarian group Jugend Rettet, which patrols the stretch of sea into which smugglers have sent more than half a million people over the past four years, said rescue boats in the area were struggling to cope.
"Despite all efforts, three people died from a sinking rubber boat," Jugend Rettet wrote on Facebook.
"We reached the capacity limit of our ship, while our crew is seeing more boats on the horizon. Currently, all vessels are overloaded."
About 72,000 migrants have arrived in Italy by sea in 2017, a roughly 20 percent increase on the same period last year, and more than 2,000 have died in the attempt, according to the International Organization for Migration.
At Europe's southern frontier, Italy has become the main destination for primarily sub-Saharan African and Bangladeshi migrants since the European Union struck a deal with Turkey which blocked a once-busy route to Greece.
Italy and the EU are trying to work with Libyan authorities to fight smugglers, but the same chaos which allowed the gangs to establish profitable businesses is hampering their efforts.