Navy and fishing crews were able to pick up 23 survivors, who came from Nigeria, Mali, Benin and Burkina Faso.
They said the pirogue, a simple open boat with plank seating of a kind used throughout Africa, had left the Nigerian town of Orong heading south towards Gabon’s economic capital, Port Gentil.
After it sank, local fishermen swiftly raised the alarm and a Cameroon naval vessel went to the rescue with the help of volunteers.
Naval ships and fishing pirogues are still searching the area trying to find other survivors.
The 23 people pulled from the sea were still under medical observation at health centres in Londji and Itongue, near the town of Kribi.
There were no details of why the boat capsized in the early hours of Wednesday morning.
It is the second such tragedy in less than a year off Cameroon. Forty-three people drowned when a boat carrying passengers from Nigeria to Gabon sank off Campo off the southern coast of the country last June.
Meanwhile, hundreds of African migrants have drowned trying to reach Spanish soil in un-seaworthy vessels.
Figures published Tuesday in the Spanish media showed that between 1,200 and 1,600 illegal immigrants who tried to reach Spain from Mauritania in tiny boats drowned in a 45-day period in late 2005.
Despite joint international action to prevent clandestine migration, thousands of people from the poorest parts of Africa seek to leave their homes, sometimes in the hope of ending somewhere where they can earn money to send back to their families.
Boat owners and desert smugglers alike make a great deal of money from offering to help such people, though the would-be emigrants risk their lives in the process.