Chaos broke out after a shooting at the ZombiCon festival in Florida left one person dead and at least four wounded.
Large crowds of attendees quickly fled the area as shots rang out during the event in downtown Fort Myers.
Video from the scene shows the immediate aftermath of the shooting as hundreds of people ran away from the gunfire.
Lt. Victor Medico of the Fort Myers Police Department told the News-Press that one person was killed and four others required treatment after suffering injuries.
No details were immediately available about the suspect or victims. Police did not immediately return a phone call, Associated Press reported.
Other reports showed police officers shouting "The party's over, let's go" as they cleared the area around the event.
NBC2 reported that a search for the suspected gunman continues. A description is yet to be released.
The incident began at 11.44pm on Saturday evening and police responded almost immediately.
The annual event attracts as many as 20,000 zombie enthusiasts and is known for its hi-jinx dress up parties which often flow onto the city's streets.
Fake accessories and guns are a common sight at Zombicon and amateur dramatics can be a big part of the horror-themed genre.
Organisers released a statement on Facebook shortly after the shooting.
Other footage from the scene, below shows the emergency services helping those injured by the attack.