Four people were killed when the metal scaffolding that holds lights and other stage equipment fell Saturday night, and a fifth died overnight at a hospital, the LA Times reported, quoting Indiana State Police Sgt. Dave Bursten.
The fairgrounds were closed following the accident, which occurred shortly before the country music duo was to take the stage before an audience of about 12,000 during an approaching storm.
Gov. Mitch Daniels said the gust of wind that toppled the stage was a "fluke" that no one could have anticipated, and insisted that precautions had been taken, the LA Times reports.
However, forecasters had warned that heavy rain and strong winds would hit the fair nearly two hours before the storm moved through, with the National Weather Service estimating winds of 60 to 70 mph, CNN reports.
"The wind just picked up and the stage just caught and the roof just caught and it went up like a sail and then it crashed forward into the people standing in the front," said a WANE-TV reporter who witnessed the incident, according to TMZ.
"There were people trapped underneath and everyone was running and screaming. They were asking any medics or nurses not to leave."
Forty-five were reported injured with anything from cuts and bruises to fractures and severe head trauma, NBC reports.
The mother of a 17-year-old who suffered a broken back said her son may not walk again.
Meanwhile, police have identified those killed in the accident as: Tammy Vandam, Glenn Goodrich, Alina Bigjohny, Christina Santiago, Nathan Byrd.
Investigators began sifting through debris of the stage on Sunday, CNN reports, quoting investigators as saying that the deaths occurred when metal scaffolding fell onto the "Sugarpit," a section usually occupied by Sugarland's most ardent fans, about four minutes after authorities took the stage to warn the crowd to seek shelter.
A post on Sugarland's Twitter account late Saturday said: "We are all right. We are praying for our fans, and the people of Indianapolis. We hope you'll join us. They need your strength."