The boat sank 10 kilometres from the coastline near the city of Sfax, a member of the coastguard said. Rescue operations are continuing.
Tunisia's national guard said at least two people are dead and 14 are missing after a boat carrying migrants sank off the Tunisian coast.
National Guard spokesman Houssameddine Jbabli said authorities rescued nine people from the boat on Tuesday and are searching for the others near Tunisia's Mediterranean coastal city of Sfax.
He said Tunisian coast guard patrols have detained 192 people and stopped 10 boats trying to take migrants to Europe over the last two days.
All those detained are Tunisian, except for three Iraqis.
The stepped-up efforts against illegal migration are coming as Tunisia mobilised more than 100,000 security agents around the country for Sunday's presidential election.
Tunisia is both a source of migrants and a transit point for other African migrants seeking to reach Europe.