A Colorado woman was among five dead stemming from a shooting early Monday at a nightclub in a popular Mexican resort.

Alejandra Villanueva was the lone American killed in the attack, her family told Fox 31 Denver. Two other Americans were injured. Fifteen were injured in all.

“She was a hard worker. She was really smart. She liked art,” her brother Roberto Martinez told the station.

Quintana Roo Prosecutor Miguel Angel Pech Cen said the four other victims in the assault were members of the security team of the BPM Festival, an annual 10-day and night electronic music festival. They were two Canadians, one Italian and one Colombian, he said.

Villanueva, 18, was killed either by an accidental fall or as a result of the stampede during the evacuation of the place.

The shooting unfolded at around 2:30 a.m. as club-goers waited in line to get into the BPM Festival’s closing party at the Blue Parrot.

The government of the Caribbean coast state of Quintana Roo said four people had been detained, but it was unclear if they included the shooter. Pech said terrorism had been ruled out.

The BPM Festival is popular with foreign tourists, especially from the United States and the United Kingdom.

The organizers posted a statement on Facebook saying the attack involved "a lone shooter."

Rodolfo Del Angel, director of police in the state of Quintana Roo, told the Milenio TV station that the shooting was the result of "a disagreement between people inside" the nightclub and that security guards had come under fire when they tried to contain the dispute.

Marcos Vazquez, 29-year-old from El Paso, Texas, told NBC News that he was with his girlfriend at the nearby La Vaquita nightclub when he saw people running by.

He said they ran into the bathroom and locked themselves inside with eight other people.

DJ Jackmaster, one of the performers at the rave, tweeted that someone stormed the club and opened fire.

A video tweeted out shows panicked club-goers running into the streets to escape the reported gunfire.

Stephen Rosado, a New York native, told the New York Daily News that he heard “at least five or six shots” and that everyone in line to get into the club was running away. He said he saw emergency personnel put two people into ambulances.

BPM officials tweeted that police investigations were under way and that everyone needed to shelter in place.

The Associated Press contributed to this report.

Click for more from Fox 31 Denver.