The manoeuvre was very similar to one made by a German rescue ship one week ago which disobeyed direct orders from port officials to moor in Lampedusa.
Television images showed migrants sitting in rows on the bow of Mediterranea Saving Humans sailing boat wearing orange life jackets.
They applauded as they docked on Saturday afternoon. There was no immediate movement to disembark.
Italy’s hard-line interior minister, Matteo Salvini, has barred all private rescue ships from entering Italian ports.
He pointed to an offer from Malta to accept the migrants from the Italian-flagged ship. But the rescue organisation said Malta was too far for its ship.