The suspected use of a pepper spray-like substance is thought to have sparked the chaos at the venue in the town of Corinaldo, near Ancona in central Italy.
At least six people, including five teenagers, have died in a stampede at a nightclub on Italy's east coast near Ancona.
The audience at Lanterna Azzurra club ran for the exits after someone sprayed a substance similar to pepper spray, AP quoted ANSA news agency as saying.
One of dead was a mother of a teenager. More than 100 other people were injured, including a dozen who were seriously hurt.
This handout picture taken and released by Italian fire and rescue service shows emergency personnel treating victims after the stampede in Corinaldo.
Ancona Chief Prosecutor Monica Garulli told reporters at the scene: "The number of tickets sold is about 1,400, compared to a capacity of about 870" people. At one point, one of the side barriers collapses under pressure and sends several people falling on each other. It wasn't immediately clear if that happened because of the stampede or was a cause of the stampede. He said that when rescuers arrived, all the doors were open. A teenage survivor told ANSA that when he tried to flee, he discovered that at least one of the emergency exits was locked.
They said 12 of the injured were in serious condition.
A teenage survivor told Italian media: "We were dancing and waiting for the concert to start when we smelt this pungent odour".
Salvini vowed that responsibility would be determined for the "six broken lives - whoever out of nastiness, stupidity or greed transformed an evening of partying into tragedy".