Gov. Mitch Daniels called the collapse of the stage at the Indiana State Fair a "fluke" event Sunday, as officials released the identities of the five people killed in the incident.

Daniels choked up during a news conference when he called the deadly collapse an "unthinkable tragedy."

"This is the finest event of its kind in America, this is the finest one we've ever had, and this desperately sad ... fluke event doesn't change that," he said.

Five people killed after strong gusts of wind caused the stage to topple at the Indiana State Fair late Saturday night.

At least 45 other concert-goers were injured when blustery winds caused the fair's stage to collapse, sending lights and other stage equipment tumbling into the audience below.

Songstress Sara Bareilles had just finished performing and the crowd was waiting for country music duo Sugarland to take the stage.

Hundreds of revellers scattered amid the chaos while other bystanders rushed to lift steel scaffolding off the injured while emergency crews set up a triage centre near the stage.

"It was horrible," concert-goer Emily Davis told Indianapolis news station WTHR. "People were running and going crazy."

The Marion County Coroner's office said on Sunday that 23-year-old Alina Bigjohny of Fort Wayne, 29-year-old Christina Santiago of Chicago, and Indianapolis residents Tammy Vandam, 42, and Glenn Goodrich, 49, died in the hours after the collapse.

Fifty-one-year-old Nathan Byrd, of Indianapolis, died in hospital overnight. Byrd is believed to be a spotlight worker who was on the stage when it collapsed.

Witnesses reported seeing several people with head and neck injuries and broken bones. Indiana State Police Sgt. Rich Myers would only offer that the injuries ranged from "slight to very critical."

At least 18 concert-goers were transported to the nearby Wishard Memorial Hospital with non-life threatening injuries, confirmed hospital spokesperson Todd Harper. He said the problems included head injuries, bone fractures and lacerations.

A 7-year-old fair attendee was among those being treated in hospital, said Harper, who didn't provide further detail.

The number of reported injuries might rise in the coming days, said Indiana State Police Sgt. Dave Burstein who explained that many concert-goers may have taken themselves to the hospital.

Cindy Hoye, the fair's executive director, told reporters Sunday that all fair workers are "very much in mourning" on what is a "very sad day at the state fair."

Early warning

A timeline released by Indiana State Police showed fair staff placed calls to the National Weather Service four times between 5:30 p.m. and 8 p.m. local time. Fair officials said Sunday they prepared an evacuation plan and notified concert-goers that they may have to evacuate the fair grounds.

Around 8:30 p.m., state troopers moved toward the grandstand to prepare for a possible evacuation, the timeline showed.

A local radio personality took to the stage moments before it caved in to warn the crowd that severe weather conditions were possible, said Indianapolis Star journalist David Lindquist.

Lindquist, who was sitting in the fifth row at the time of the collapse, said the announcer gave the crowd instructions on what to do if an evacuation was necessary.

"Moments later this gust of wind came and crumpled the rigging," he told CTV News Channel on Sunday.

Lindquist said there was a cement slab that is used as a stage throughout the year, but a large metal framework was added to the stage during the 16-day fair. He said each band that played attached its own speakers and equipment to the framework.

Witnesses reported seeing a dark sky with short blasts of lightning just before the stage's collapse. Despite the evacuation warning, Lindquist said many concertgoers chose to stay put and wait out the weather.

The collapse was particularly treacherous because there was an exclusive pit for special guests sitting next to the stage, said Lindquist.

"There was an actual VIP pit close to the stage," he said. "The tragic thing is, in this instance, it put a higher concentration of people in harm's way."

Witnesses near the pit reported seeing a towering wall of dirt, dust and rain hit the fairgrounds before the collapse.

Concert-goer Jessica Alsman told The Associated Press that the towering, metal stage "kind of wobbled at first" before crumpling into the audience.

Faced with an initial blast of wind, Alsman and her friends grabbed each other and formed a chain. The group of four wasn't expecting what happened next.

"You can't imagine," she said. "We just thought it was going to rain or something."

After the storm

In the wake of the incident, fair officials cancelled all festival activities scheduled for Sunday.

Instead, emergency crews continued to search through the wreckage on the Indiana fairgrounds to ensure there were no other injured concert-goers who wandered off after the collapse.

The fair, which was slated to run through Aug. 21, is expected to resume Monday with a service honouring the victims.

Jennifer Nettles, the lead singer for Sugarland, said that members of the country band were heartbroken for the fans and their families in Indiana.

"We hold those injured in our prayers at this very sad time. There are no words. It is tragic," Nettles said in a statement.

With files from the Associated Press