At least 127 people are feared drowned after a boat sank off Cameroon's Atlantic coast near the port of Kribi.
Local fisherman discovered the shipwreck, raised the alarm and rescued 23 people found clinging to flotsam.
The BBC's Randy Joe Sa'ah says survivors taken to Kribi hospital are said to be in a critical condition.
Some survivors say 150 people were on their way from the port of Oron in Nigeria to Gabon's Port Gentil when the boat was engulfed by big waves.
But a local Red Cross official, Francois Mahouwa, quoted others as saying there could have been twice that number.
An official rescue team is searching for survivors and trying to recover bodies.
Cameroonian authorities have said they will cover the medical bills of the survivors.
The passengers included nationals from Nigeria, Burkina Faso, Benin, Mali and Niger on their way to Gabon to look for work.
The boat, which was made of wood, is thought to have broken up in high seas.
Passenger boats are often overloaded and in bad repair, our correspondent says. This is the third boat to have gone down in bad weather in the Gulf of Guinea in the past year.
Thousands of Africans leave their homes each year for Europe and other parts of Africa looking for work or hoping to start a new life.