The death toll from the sinking of a migrant boat off the coast of Madagascar on its way to the French island of Mayotte in the Indian Ocean has risen to 34, and the death toll from a ferry sinking off the coast of Gabon has risen to 21.

Authorities in Madagascar earlier gave the first toll of 22 migrant deaths on Sunday night, before announcing that the number of shipwrecked carrying about 60 migrants had risen to 34 off the northern coast of the Great Island.

The director of the Ports, Seas and Rivers Authority, Jean-Edmond Randriyanantininaina, said the bodies recovered by authorities on Tuesday, including three of children, were "in an advanced state of decomposition".

Two search warrants were issued for two Malagasy nationals, a 47-year-old man and woman, accused of smuggling migrants on board.

Smugglers use small motorized fishing boats, and drownings are regularly recorded on the sea route linking Comoros or Madagascar to Mayotte.

Many African and Comorian migrants try every year to reach the archipelago, half of whose population is foreign. The Comoros island of Anjouan is just 70 kilometres from Mayotte.

A ferry sinks on the coast of Gabon

On the other hand, the Public Prosecution in Gabon announced on Tuesday that the death toll of the sinking of a small ferry off the coast of the capital Libreville rose to 21 dead, after the recovery of 15 additional bodies while the search for 16 missing continues.

124 of the 161 passengers and crew on board the Easter Miracle, which sank on Thursday night near the coast, rescue teams said.

The ship, carrying passengers and cargo, was on a voyage between Libreville and the port of Port Gentile.

Prosecutor André Patrick Robonat said an additional 15 bodies "recovered from the water were in the ship and, thanks to the intervention of divers, were exhumed, all wearing life jackets."

An investigation into the incident has been opened and the government announced on Monday the suspension of four administrative officials as a precautionary measure, while the Public Prosecution also spoke of placing people under investigation and arresting others.