Rescuers found the victims' bodies on beaches by the capital Libreville, the interior ministry said.
The drownings were caused by an "increase in the tides linked to climate change," the ministry added.
High tide in Libreville usually varies between 1.60 and 1.80 meters, but since Sunday, the water levels have exceeded 2,50 meters, the marine weather service said on Tuesday.
The Libreville coastline is a popular spot for visitors as temperatures rise with the approach of the spring equinox, which brings higher tides.
Despite the warnings, the Leon MBA High School beach, where some of the bodies were found, remained open and unmonitored on Wednesday afternoon, an AFP journalist saw.
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