The attorney general of Quintana Roo state said that four of the dead appear to have been part of the security detail at the 10-day BPM electronic music festival.
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Miguel Angel Pech said the shooting occurred about 2:30am at the Blue Parrot nightclub, one of the BPM Festival's venues in Playa del Carmen, just south of Cancun.
Pech said a lone gunman apparently entered the nightclub and began to exchange fire with another person inside.
Festival security personnel tried to stop the shooting and came under fire.
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Pech said it was not a terrorist attack.
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He said 20 bullet casings from three different pistols had been found at the scene, and said it was unclear if the security detail had been armed or fired any of the weapons.
The shooting apparently caused a rush of people heading for the exits at the beach-side club, and the lone female victim was apparently killed during the stampede.
Pech said 15 people were injured, included one Mexican woman who was seriously injured.
He said five of the injured -including two U.S. citizens and one Canadian -had been treated for less serious injuries at local hospitals and released.
He said three people had been detained nearby, but it was unclear if they had been involved in the shooting.
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Rodolfo Del Angel, director of police in the state of Quintana Roo, told the Milenio TV station that he shooting was the result of "a disagreement between people inside" the nightclub and said security guards had come under fire when they tried to contain the dispute.
The BPM Festival posted a statement saying four people had been killed and 12 injured in an attack that involved "a lone shooter."
BPM wrote that "the violence began on 12th street in front of the club and three members of the BPM security team were among those whose lives were lost while trying to protect patrons inside the venue."
Playa del Carmen has largely been spared the violence that has hit other parts of Mexico.
Canadian officials could not immediately confirm if any of their citizens were among the victims in the shooting.