The boat, which broke up in high seas, was discovered by a fisherman on Thursday who alerted his colleagues and people living in coastal villages who rushed to the scene to find bodies floating on the water and survivors hanging on to flotsam.
Gregoire Mvodo, a local official in Kribi, said: "By the time we called security agents and reached the area, a group of fishermen and villagers had already mobilised and were trying to rescue passengers.
"Unfortunately almost all of them perished."
The boat was travelling from the eastern Nigerian port of Oron to Port Gentil in Gabon, carrying passengers from Nigeria, Burkina Faso, Benin, Mali and Niger who had set off to find work in Gabon.
The local Red Cross co-ordinator in the region around Kribi, Francois Mahouwa, said the boat had officially been carrying 150 passengers but that some survivors said twice that number were on board.
"The Nigerians said there were 150 on board but the Burkinabe, the Beninois and those from Niger said there were nearer 300," he said.
Many of the vessels plying trade and passenger routes off West Africa's shores are poorly maintained and overcrowded, making it difficult to estimate how many people are travelling.
Mahouwa said 22 men, three women and a young girl had been saved and were being given food, shelter and medical care for minor injuries in the village of Londji, around 15km north of Kribi port.
He said it would be difficult to establish a final death toll as those bodies that had been recovered were quickly being buried in communal graves by villagers along the coast. The search for remaining survivors had been called off.
There have been several shipping disasters in recent years in the Gulf of Guinea, where passengers often travel in overloaded vessels lacking communications, particularly on the route from Nigeria used by labourers going to work in Gabon.
About 30 people drowned after a boat travelling from Nigeria to Gabon sank off Kribi in high seas last July.
A group of 68 children thought to be victims of child trafficking were rescued from a sinking ship off Cameroon in 2001. At least 280 people drowned when their overcrowded boat sank during a trip from Nigeria to Gabon in 1998.