(CNN) -- They came for a night of music and dancing. They left by fleeing past wounded clubgoers lying on a bloody floor.
Shortly after 1 a.m. Sunday at the packed Cameo Night Club in Cincinnati, a DJ called for security over and over, one man recalled later.
Four off-duty police officers were outside in the parking lot.
To get in, clubgoers had been searched with an electronic wand to detect hidden weapons.
Still, the witness told CNN affiliate WLWT that he heard about 20 gunshots in the club.
One person was killed and 15 wounded. Police said several people had been able to sneak guns into the club and they believe more than one person was involved in the shooting. They said it might have developed from a dispute that started earlier in the day.
The shooting was not related to terrorism, authorities said.
Police identified the slain man as O'Bryan Spikes, 27.
Several victims were undergoing surgery, Cincinnati Police Sgt. Eric Franz told CNN Sunday morning. Police do not have any suspects in custody but are interviewing witnesses.
'A lot of chaos'
Cameo is in the former home of a gay bar called Adonis, which closed in 2012.
It is in the city's East End area, on the Ohio River Scenic Byway near Cincinnati Municipal Airport - Lunken Field, amid used auto parts yards and marinas.
Cameo hires police officers for extra security. Two officers were stationed at the club's entrance and another two in the parking lot, Franz said.
Officers in those situations are allowed to provide security only outside the clubs, Police Chief Eliot Isaac said later. Clubs are responsible for their internal security.
A man who was inside told CNN affiliate WLWT that he heard the DJ calling for security, although the music hadn't stopped.
"It was just a lot of chaos, obviously, when the shots went off," Cincinnati Police Department Capt. Kimberly Williams said. "People (were) just trying to get out of harm's way."
To leave the club, some partiers had to flee past injured people on the floor.
'Chaotic crime scene'
Police found a "chaotic crime scene" as they looked for witnesses, many of whom took off when the shooting started, said Cincinnati Assistant Police Chief Paul Neudigate.
"Everyone that we can identify is being interviewed," he said.
The packed parking lot and the crowds trying to drive away hindered fire rescue teams, Assistant Fire Chief Roy Winston said.
"You had a mass group of people leaving the scene," Winston said.
Police are hoping witnesses will come forward to help identify suspects.
Some of the injured drove themselves to area hospitals, police said.
One patient was treated for a gunshot wound and released from Anderson Hospital, said Nanette Bentley, hospital spokeswoman. Another person walked into West Hospital with a non-gunshot injury and was treated and released, Bentley said.
'Just going to have a good time'
Cincinnati Mayor John Cranley said his city is "deeply saddened by this tragedy" and urged community members to work together.
"People were just going to have a good time and ended up getting shot," he said. "That is totally unacceptable.
"This is a tragedy that has struck other communities and now it has struck Cincinnati. Our hearts are broken but our spirit is not."
Club has had 'challenges in the past'
The Cameo nightclub allows admission to anyone over the age of 18 on Friday nights. Saturday nights are 21 and above and promoted as "grown and sexy" night.
Cameo has a history of violent incidents, WLWT reported.
"We are aware of it. It (the club) has had some challenges in the past," Neudigate said.
Multiple assaults were reported at Cameo from 2014 to 2016, affiliate WXIX reported.
Worst US mass shooting so far this year
The incident is the worst mass shooting (for total number of victims) so far in 2017, according to Gunviolencearchive.org. There have been 71 in the US this year.
In Cincinnati alone, there have been at least nine since 2013. The most recent was February 28, when six people were shot at an apartment building in the Northside neighborhood.
The Bureau of Alcohol, Tobacco and Firearms is helping Cincinnati police with this investigation.
"Saddened to learn about last night's shooting in Cincinnati," Ohio Gov. John Kasich tweeted. "Our prayers are with the victims and families of all of those involved.
"I've instructed our administration to offer any assistance the state can provide."