Six people were killed and dozens injured in a stampede at a nightclub on Italy's Adriatic coast Saturday, authorities said.

An Italian fire brigades official told NBC News that it is believed the stampede was the result of a panic sparked by someone using pepper spray at the venue in the town of Corinaldo. Some 800 people were at the event.

A police official said a popular Italian rapper, Sfera Ebbasta, was performing at the Lanterna Azzurra nightclub Saturday night.

#Corinaldo (AN) #8dic 1:00, squadre #vigilidelfuoco impegnate nel soccorso in una discoteca. Forse per la dispersione di una sostanza urticante, ragazzi fuggono per il panico calpestandosi. Sei purtroppo quelli deceduti, decine feriti pic.twitter.com/NvII0jD7oe — Vigili del Fuoco (@emergenzavvf) December 8, 2018

The dead included three girls, two boys and a woman who had accompanied her daughter to the venue, police said. At least 12 people were in serious condition, police said, while another 40 sustained less serious injuries.

Firefighters gave first aid to survivors, stretched out on the road outside the club, in the aftermath.

A teenager told the ANSA news agency that at least one of the emergency exits was locked when he tried to flee.

Ancona Firefighters Cmdr. Dino Poggiali told Italian media that it was too early to know if any safety violations at the club played a role in the incident but an investigation will be conducted.

The bodies of the trampled victims were all found near a low wall inside the disco, he added.

"It was a mess. The bouncers were getting the persons out," an unidentified witness told RAI state radio. "I went out the main door. People fell, one after the other, on top of each other. Absurd."

Another witness told RAI they smelled something acidic inside the club moments before running out. Police said the case is "complex" and it's unclear what, if any, substance was sprayed.

Performer Sfera Ebbasta wrote on Twitter that he was "deeply pained" by the tragedy, thanked rescuers and offered his "affection and support" to the families of the dead and the injured. Out of respect to them, he cancelled some promotional appearances.

The rapper added he wanted everyone to "to stop and think how dangerous and stupid it is to use pepper spray in a discotheque."

Italy's Interior Minister Matteo Salvini tweeted that a moment of silence would be held Saturday at the Piazza del Popolo in Rome to honor those who died. "One can't die this way," he said, adding that those responsible for the incident will be held accountable.

The country's head of state, President Sergio Mattarella, demanded "full light be shone on what happened, ascertaining any responsibility and negligence."

"Citizens have the right to safety wherever they are, in workplaces as well as places of entertainment," Mattarella said in a statement. "Safety must be assured with special commitment in places where crowds gather, through rigorous inspection and checks. One cannot die this way."

At the Vatican, Pope Francis bowed his head in silent prayer after he told some 30,000 pilgrims and tourists in St. Peter's Square that he was praying "for the young people and the mamma" as well as for the many injured.

Italian high schools are usually open on Saturdays, but schools were closed this weekend for the Dec. 8 national holiday of the Immaculate Conception. That could have made it more likely that young teenagers were at the disco.