The coast guard rescued 336 people aboard a boat near Porto Empedocle in Sicily and escorted them ashore, where most of them fled from police.
The migrants said they were all from Eritrea.
Dramatic video images shot from a border guard vessel showed the migrants including women and children being helped off a heavily overcrowded boat at night.
A second boat with 233 people aboard was also spotted by a navy vessel and taken to the tiny island of Lampedusa, Italy's southernmost point and a major arrival point for migrant boats from Libya and Tunisia.
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"I want to be a human like everybody. In Syria, everything is destroyed," one of the migrants told news channel SkyTG24. Another said the journey had "lasted 10 days and we ran out of water".
Local coast guard official Luca Sanciglio said: "We were told about the impending landing by a fisherman who spotted them. The boat was not stable so we had to ferry them to the shore."
"We have a duty to rescue everyone 24 hours a day and that includes immigrants," he said.
Most of the thousands of economic migrants and refugees who have landed in Italy in recent months have landed in Libya from other parts of Africa.
Some 350 migrants -- many of them from Egypt and Syria -- arrived on four boats in Sicily yesterday.
Calmer weather conditions and growing unrest in north Africa have led to a surge in migrant arrivals in recent weeks.
Italy's interior ministry said 24,277 migrants landed in Italy in the 12-month period between August 1, 2012, and August 10, 2013.