A shooting at a Florida Zombicon event killed one person and injured four others, the Fort Myers Police Department said on Sunday in a social media post.
Police asked attendees to share smartphone video from the incident at an event expected to draw more than 20,000 people.
The shots were fired shortly before midnight on Saturday at the festival in downtown Fort Myers on the state's west coast, according to the News-Press newspaper.
The shooter remained at large on Sunday morning, the newspaper reported, noting that crowds of people were seen running through the area immediately after the shooting.
The four who were injured sustained non-life threatening injuries, the News-Press said, citing police.
The annual event brings zombie-themed activities, including music and performance artists, to the streets of Fort Myers, according to its website. It comes during a month in which communities across the United States are celebrating the Halloween holiday, including many popular events for adults offering spooky thrills celebrating the revival of the dead.