At least 20 migrants have died after their boat capsized in the Mediterranean off the coast of Tunisia, officials say.

Tunisian coastguard boats retrieved the bodies off the coastal city of Sfax in central Tunisia on Thursday.

A search is continuing for at least 20 more people who are still missing.

Five survivors were rescued. The boat, with an estimated 45 people on board said to be from sub-Saharan Africa, was attempting to reach Italy.

Overloaded and in poor condition, the vessel faced strong winds that may have contributed to the sinking, National Guard spokesman Ali Ayari told the Associated Press.

Thousands of migrants attempt to cross the Mediterranean to Europe every year, with parts of Tunisia and Libya key departure points.

Many of the migrants are from sub-Saharan African countries fleeing economic hardship and crisis at home.

The number of migrant journeys from Tunisia has declined since 2011, when a revolution overthrew the country's former leader Zine al-Abidine Ben Ali.

But illegal crossings from Tunisia to Europe increased by more than 150% in the first four months of the year, compared with the same period in 2019, according to the United Nations refugee agency.

Tunisia's interior ministry said 8,581 migrants were intercepted attempting to cross the Mediterranean between January and mid-September this year.

Italy has been struggling to deal with daily arrivals of hundreds of migrants to its southern shores, a task complicated by the ongoing coronavirus crisis.