At least 40 migrants drowned in a shipwreck in waters off Tunisia as they tried to cross the Mediterranean to Italy, United Nations and Tunisian officials said on Friday.

The Tunisian coastguard had so far recovered 21 bodies, all African migrants, and rescued three people, Tunisian officials said. The dead included at least one child.

"The boat sank during a trip that started late on Thursday from Sfax. So far, the coastguard has recovered 21 bodies and the search is still continuing," said Mouard Mechri, director of Tunisia's civil protection service.

The coastline near the port city of 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.

Last month 39 migrants died off Sfax in a similar accident.

The UN migration agency International Organization for Migration and the UN refugee agency United Nations High Commissioner for Refugees said in a statement: "This tragic loss of life underscores once again the need to enhance and expand State-led search and rescue operations across the Central Mediterranean."

Some 290 people have lost their lives in such shipwrecks this year, they said.