Around 3,000 people had been saved from dangerous boats on Saturday, as good weather leads to greater volume of journeys
Seven migrants died in the Mediterranean off the coast of Libya while trying to reach Europe on Sunday, an official of a rescue ship said.
Reuters had earlier erroneously reported that 20 people had died.
Chris Catrambone, co-founder of the Malta-based Migrant Offshore Aid Station (MOAS), said "the discrepancy was due to confusion" in communication between two ships involved in the rescue operation.
On Saturday, the Italian coastguard and other boats rescued around 3,000 migrants from unseaworthy boats off the Libyan coast.
Good weather is encouraging more people to make the journey, an NGO said.
In all, 35 rescue operations were launched during the day, with 15 of them still underway as night fell, the coastguard said.
German NGO Jugend Rettet, which took part in the rescue operations on Saturday, said 3,000 people had been plucked to safety during a particularly busy day due to the fine spring weather in the Mediterranean.
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Jugend Rettet spokeswoman Pauline Schmidt told AFP that a further 1,000 people remained to be rescued from inflatable dinghies and other craft, with the rescue ships reaching capacity.
Other, mainly non-governmental, boats were expected to arrive in the area to help the rescue operations, she said. "We have never had to deal with so many people at the same time."
On Friday, rescue vessels worked flat out to rescue over 2,000 people from flimsy dinghies.
So far this year 666 people have been logged as dead or missing off the Libyan coast.
Throughout last year more than 5,000 people perished, according to the International Organization of Migration