Dreadful Indianapolis stage collapse: video
The incident occurred at around 01:00 GMT, when the band Sugarland was set to perform. A strong gust of wind caused the rigging that holds lights and other equipment to fall over on to fans, mostly in the VIP section close to the stage.
Winds of up to 96 km/h were registered at the site, local newspaper reported.
Witnesses at the scene said before the accident an announcer had alerted them that severe weather was possible and gave instructions on what to do if an evacuation was necessary. But the same announcer said concert organizers hoped the show would go on, and many fans stayed put.
Hundreds of concert-goers rushed to tend to the injured, lifting the steel scaffolding off them and providing medical care.
It is the first tragedy during such a public event in the State of Indiana since 1963. On Halloween night that year, during a "Holiday on Ice" skating exhibition at the Indiana State Fairgrounds Coliseum, a propane gas explosion killed 74 people and injured nearly 400.