Some 20 African migrants were found dead Thursday after the boat that was attempting to smuggle them to Europe sank in the Mediterranean Sea, Tunisian authorities said.

Five survivors were rescued and the Tunisian navy is searching for up to 20 others still believed to be missing. Tunisian coast guard boats and local fishermen found the bodies off the coastal city of Sfax in central Tunisia, Defense Ministry spokesperson Mohamed Ben Zekri told The Associated Press (AP).

According to the survivors, the boat was carrying about 40 or 50 people heading toward Italy, Ben Zekri said. It was believed to be carrying migrants primarily from sub-Saharan Africa, he said. Tunisian navy units were on the scene to search for any more survivors.

The boat was heading to Italy from the Sidi Mansour district of Sfax, a spokesperson for the interior ministry, Khaled Hayouni, said, as quoted by Agence France-Presse (AFP).

Tunisia is just a few hundred kilometers (miles) from mainland Europe and has long been a launchpad for illegal migration to the continent. Departures by desperate migrants seeking a new life in Europe peaked in 2011 following the revolution that overthrew Tunisian dictator Zine El Abidine Ben Ali.

Although numbers have dropped significantly in recent years, illegal crossings from Tunisia to Europe jumped by more than 150% from January to April compared to the same period last year, according to the United Nations High Commissioner for Refugees (UNHCR). Most of the migrants are from sub-Saharan African countries fleeing economic hardship and crisis at home.

According to the Tunisian interior ministry, 8,581 migrants were intercepted after setting off on the perilous Mediterranean crossing between January and mid-September. Of those, 2,014 were non-Tunisians.

Earlier this month, the Tunisian navy said it had intercepted 93 African migrants after their boat broke down off Sfax during an attempt to reach Italy.