The events occurred in Canaan, a neighborhood on the outskirts of the capital, currently under the control of armed groups.
Videos posted on social networks show the bloody corpses of faithful, and alleged gang members can be heard claiming responsibility for the crimes. In addition, a dozen people were kidnapped, according to local press reports.
The march was organized by pastor Marcorel Zidor, with the aim of evicting the Canaan gang, and was attended by hundreds of faithful.
His followers marched with sticks and machetes from the Caradeux road towards Canaan, but in Rosenberg they came under fire from members of an armed group.
Press outlets say that the real number of victims may be higher, while Internet users on social networks call on the authorities to arrest the pastor who convened the demonstration.
The Canaan area has been under the control of gangs for months and was the scene of several massacres in the last year.
Violence in Haiti has spiked after a brief lull in the aftermath of the Bwa Kale operation in which hundreds of suspected gang members were lynched since late April.
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