The "Very Holy Church of Jesus Christ of Bename", a controversial sect which claims thousands of members, had told followers to spend Saturday in a sealed room praying for the holy spirit.
"These patients were all poisoned with carbon monoxide in the Porto Novo and Adjarra areas," the health official, who asked to remain anonymous, told AFP.
"There are currently five deaths and nine people in intensive care," the official added.
"Some may have fallen on the embers placed in the rooms where they locked themselves for the prayer."
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The church was founded in 2009 by a young woman, Vicentia Tadagbe Tchranvoukinni, often referred to as "Perfect", who says she is "God the Holy Spirit."
Tchranvoukinni regularly vilifies other faiths, including voodoo -- an official religion in the tiny West African nation -- and Roman Catholicism, stoking tension in the community.
On January 8, violent clashes broke out between residents in the southern town of Djime and cult followers who had "insulted and offended" traditional leaders during a "mission of evangelisation", according to one local resident.
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