The boat's passenger list was not immediately available.
Frequent accidents
It was not immediately clear who the passengers were. Many living in Guinea's coastal communities use open boats for transportation due to poorly-maintained roads.
Wednesday's incident comes just over a week after 65 people were killed when a bridge collapsed under the weight of a truck packed with passengers and goods as it travelled to a market in the country's remote southeast.
Similar accidents off the West African coast have occurred in recent years involving migrants fleeing poverty by trying to illegally reach Spain's Canary Islands to find work in Europe, risking voyages of up to 2,000 km.
About 6,000 people died en route to the Spanish archipelago last year alone, according to Spanish officials.
Guinea is the world's leading exporter of bauxite, used to make aluminium but despite its mineral wealth, the country is mired in poverty with most of its nearly 10 million people surviving on less than $1 a day.