Officials had initially said six people were known dead, but later lowered the figure.
Civil protection official Jean-Michel Sabbat said the search was suspended late Saturday afternoon and will resume Sunday.
He said the boat overturned en route from Anse a Pitre, near the border with the Dominican Republic, to the southern peninsula city of Jacmel.
Twenty-two survivors were rescued. Sabbat said rough estimates indicated that perhaps as many as 60 people were aboard the vessel.
Officials could not immediately say what kind of boat it was or what caused it to overturn.