A coastguard spokesman said it appeared many people had left the Libyan coast trying to make the perilous voyage across the sea to Europe as the weather improved.
“We saved a total of about 4,500 people in about 40 rescue operations,” the spokesman told AFP, adding the operations were continuing and the number may rise.
A body was found on board one of the rubber dinghies, he added.
Most of the migrants were on the dinghies, while two wooden boats were being used by Libyan people traffickers, the spokesman said.
“We registered a large number of voyages today, after several days of bad weather at sea had stopped people leaving Libya,” the spokesman said.
More than 10,000 people have died crossing the Mediterranean to Europe since 2014, according to UN figures issued earlier this month after a spate of deadly shipwrecks.