At least 4,000 migrants were on Thursday rescued at sea by Italian coastguards near the island of Lampedusa.
An unknown number of people are believed to have died after their vessel sank before help could arrive.
The total number of migrants Italy has helped rescue since Monday now stands at more than 10,000 – a sign that Europe’s immigration crisis is far from over.
Thursday’s incident comes on the heels of yet another vessel capsizing on Wednesday.
Reports indicated that the trawler overturned when people rushed to one side when they spotted a rescue ship.
500 people were rescued and seven bodies were recovered.
Thursday’s shipwreck was the second in two days as sea crossings to Europe accelerated with migrants taking advantage of the good weather.
Speaking to the media last month, Italy’s defence minister, Roberta Pinotti, said a Nato-led anti-smuggling mission could be in operation as early as July as other European countries tighten screws on illegal migrants
Europe’s worst immigration crisis since World War Two has led to more than 8,000 deaths in 2-and-half years, the International Organization for Migration estimates.