"The boat sank during a trip that started late on Thursday from (the town of) Sfax... So far, the coastguard has recovered 21 bodies and the search is still continuing," Mouard Mechri, director of Tunisia's civil protection service, told Reuters.
Last month 39 migrants died off the coast of Sfax, a Tunisian port city, in a similar accident.
The coastline near Sfax has become a major departure point for people fleeing conflict and poverty in Africa and the Middle East and seeking a better life in Europe.