Fifteen Tunisian migrants are missing after their boat sank in the Mediterranean during an attempt to reach Europe, authorities said Wednesday.

The boat carrying 19 Tunisians sank Monday night, said a statement by Tunisia's National Guard, which oversees the coastguard.

Four migrants were rescued by a fisherman after the boat sank, while the search for the remaining 15 continued Wednesday morning, the statement added.

Tunisia, whose coastline is less than 150 kilometres (90 miles) from the Italian island of Lampedusa, has long been a favoured stepping stone for migrants attempting the perilous sea journey.

Last week, 32 migrants from sub-Saharan Africa drowned while attempting the crossing.

The number of departures of African migrants has intensified after President Kais Saied made a fiery speech on February 21 claiming that illegal immigration was a demographic threat to Tunisia.

The North African country is in the grip of a long, worsening economic crisis that has pushed many of its citizens to take desperate measures in search of better lives abroad.