Authorities in Haiti said on Sunday that at least 30 people were killed in a stampede at a rural site in the north of the country, warning that the death toll could rise.

Jean Henry Petit, head of civil protection in the northern region, said the incident occurred at the Citadelle Laferrière, a historic fortress dating back to the early 19th century following Haiti’s independence from France.

He noted that the UNESCO World Heritage site was crowded with students and visitors attending an annual celebration at the location.

The heavy congestion led to the deadly stampede, while authorities continue efforts to assess the full extent of the casualties and investigate the circumstances of the incident.