Six people, including five teenagers, died and dozens were injured in a stampede when panic broke out during a rap concert at an Italian nightclub early Saturday.

"The cause may have been the dispersal of a stinging substance, the young people fled and trampled over each other. Sadly, six people died and dozens are injured," the fire service said in a statement on Twitter.

The victims include five people under the age of 18 -- three girls and two boys - and an adult woman who accompanied her daughter to the concert. 

Local fire chief Dino Poggiali said that 14 of the injured were in a serious condition, and 40 less serious.

As the crowd panicked, people ran for the three emergency exits, one of which led to a small bridge and the car park.

The force of the fleeing crowd made a railing collapse and dozens of people fell, crushing those at the bottom of the pile, according to a preliminary investigation.

Grainy mobile phone footage appeared to show part of a walkway collapsing, sending dozens of people tumbling down.

Ironically, those who remained inside the nightclub were unharmed.

"We were dancing and waiting for the concert to start when we smelt this pungent odour," a 16-year-old boy who was taken to hospital told the media.

"We ran to one of the emergency exits but we found it blocked, the bouncers told us to go back."