Defense Ministry spokesman Mohamed Zekri said the boat carrying migrants sank near the Sfax area on Tunisia's southeastern coast on Monday. He said workers at a local oil field alerted authorities after seeing the boat sink.

Several units of the Tunisian navy have been deployed in the coastal area to rescue and search for the missing.

Flavio Di Giacomo, a spokesperson for the Mediterranean coordination office of the International Organization for Migration (IOM), said on Twitter that all 33 migrants rescued alive off the coast of Tunisia were Bangladeshis. The boat, carrying migrants, set sail from Java, Libya, on Sunday.

However, the nationalities of the deceased could not be immediately ascertained.

Riadh Kadhi, a spokesman for the IOM in Tunisia, said the boat had set sail from Libya with about 90 people on board, according to surviving migrants.

Libya is one of the starting points for European migrants to cross the perilous Mediterranean Sea. Immigrants often choose the Mediterranean sea route to escape from poverty or conflict and travel to various European countries.

This is the fifth boat sinking off the coast of Tunisia in the past few months. At least 17 migrants drowned off the coast of Tunisia earlier this month. Two of them were rescued alive.

The country's state news agency TAP said the navy rescued 113 people from another boat off the coast of Tunisia on Monday morning. The migrants are from Bangladesh, Morocco and sub-Saharan Africa.