Jean Henri Petit, head of Civil Protection for Haiti's Nord Department, said the stampede occurred at the Laferriere Citadel, an early-19th-century fortress built shortly after Haiti's independence from France.
One of Haiti's most popular tourist attractions, the fortress was packed with students and visitors on Saturday who had come to participate in the annual celebration of the UNESCO World Heritage site, Petit added.
The Prime Minister Alix Didier Fils-Aimé said in a statement that he "extends his sincere condolences to the bereaved families and assures them of his profound solidarity during this time of mourning and great suffering."
He added that "many young people" were in attendance at the Citadel's celebrations, although it is unknown who died and the prime minister's statement did not give an estimate of the death toll.
Petit said the stampede occurred at the entrance to the site, adding that the rain further exacerbated the disaster, Reuters reported.
The deadly stampede comes as Haiti is grappling with widespread violence by gangs that have massacred civilians, as well as an increasingly deadly crackdown by security forces.