At least 80 migrants are feared dead after their boat sank off the Tunisian coast, International Organization for Migration (IOM) spokesman Flavio Di Giacomo wrote on Twitter Thursday.

"A shipwreck occurred off the Tunisian coast, 4 survivors have been rescued and brought to Tunisia. They said that their dinghy was carrying 86 people. About 80 migrants are feared dead," he tweeted.

The incident took place on Wednesday off Tunisia's southern town of Zarzis, Mongi Slim, the head of the Tunisian Red Crescent branch in the southern province of Medenine, said.

He told dpa that the four survivors had been transferred to a migrant sheltering center in Zarzis and one of them later died at a local hospital.

The boat had set sail on Monday from neighboring Libya on a Europe-bound journey, Slim said, citing coastguard sources.

At least 65 migrants drowned last May when their boat capsized off the Tunisian coast after they had left Libya hoping to reach Europe.