A preliminary report by local civil protection authorities suggested a higher toll, reporting 17 dead and 19 injured.
Armed members of the Gran Grif gang attacked the Jean-Denis area at about 3am, local civil protection authorities said.
The attack follows United Nations reports that more than 2000 people were recently displaced by armed raids in nearby Verrettes, prompting residents in Petite-Riviere to flee their homes.
The Artibonite department, a key agricultural area, has been the scene of some of the country's worst violence as gang conflict spreads beyond the capital Port-au-Prince.
In March, the United States offered a reward of up to $US3 million ($A4.4 million) for information on the financial activities of the Gran Grif and Viv Ansanm groups.
The US has designated both, which represent coalitions of hundreds of gangs, as terrorist organisations.
Haitian security forces, supported by a United Nations-backed international mission and a US private military company, have intensified operations against gangs that control most of the capital.
However, authorities have yet to arrest a major gang leader.
More than a million people have been displaced by the conflict with gangs, which has exacerbated food insecurity, and close to 20,000 have been reported killed in Haiti since 2021.
The death toll has climbed every year.
