Pope Francis has praised southern Italy for its efforts in welcoming migrants, calling the region an "example for the entire world" and commending the "courageous" Italian coastguard, the Vatican said Monday.

In a video message broadcast on Sunday evening, the pontiff thanked the members of the Italian coastguard who have played a pivotal role in migrant rescue operations in the Mediterranean.

"You are courageous men and women, instruments of hope brought by Jesus," he said.

He added that "the south of Italy has been an example for the whole world".

From the Vatican the pope symbolically lit the nativity scene in front of the basilica in Assisi, some 300 kilometres (190 miles) north of Rome.

The Assisi Christmas tree sits next to a manger placed inside a boat which brought migrants from Tunisia to the Italian island of Lampedusa, a hub for migrant arrivals.

Via video, Francis told migrants gathered at the site in Assisi to keep their "heads high in the hope of the Lord", even if their "hearts were heavy".

On Sunday the Italian coastguard said that more than 4,600 people have been plucked to safety from unseaworthy boats off the Libyan coast as they attempted the perilous journey across the Mediterranean.