Associated Press

INDIANAPOLIS (AP) -- A stage collapsed during a powerful storm at the Indiana State Fair on Saturday, sending steel scaffolding into the terrified crowd below and killing at least four people among fans awaiting a performance by the country band Sugarland.

The collapse came moments after an announcer warned of the advancing storm and gave instructions on what to do in event of an evacuation. Witnesses said a wall of dirt, dust and rain blew up quickly as a gust of high wind toppled the rigging. People ran amid screams and shouts, desperate to get out of the way.

Hundreds of concert-goers rushed afterward amid the chaos to tend to the injured, many with upraised arms seeking to lift heavy beams, lights and other equipment that blew down onto the crowd. Many of the injured were in the VIP section closest to the stage. Emergency crews set up a triage center in a tunnel below the grandstand at the Indianapolis fairgrounds.

About 40 people were injured, including at least one child, WTHR reported. Witnesses reported seeing many people with head and neck injuries and broken bones.

Todd Harper, spokesman for Wishard Memorial Hospital in the city, said later Sunday that at least 18 patients were brought in. He said their problems ranged from head injuries and bone fractures to lacerations and other cuts and bruises. He said those injuries were not life-threatening and conditions ranged from fair to critical.

One was a 7-year-old child, he said, but didn't elaborate further.

"We set up a command center and a page was sent out to staff to call the command center," he said, adding the hospital hadn't seen such a sudden influx of patients since a tornado outbreak in 2000. "This was unusual. We can't think of an incident that compared to this mass of people" arriving.

Indiana State Police 1st Sgt. Dave Bursten said the number of injured could rise because some people may have taken themselves to hospitals.

Bursten said the injuries ranged from cuts and scrapes to "very serious injuries" and that it was a "very likely possibility" that the death toll could also climb.

Emergency crews continued to search the fairgrounds early Sunday to ensure there were no other injured concert-goers who might have wandered off after the collapse, Bursten said.

Fair officials canceled all activities Sunday. The fair, which runs through Aug. 21, was expected to resume Monday with a service honoring the victims, he said.

Bursten said emergency personnel and fair officials were monitoring the weather because a severe storm had been expected to hit the area around 9:15 p.m. But the storm hit shortly before 9 p.m.

He said preparations were being made to evacuate the facility but that the "significant gust of wind" struck the stage rigging that holds lights and other equipment before the evacuation plan was activated.

"As we all know, weather can change in a very rapid period of time," he said.

Concert-goers said the opening act by Sara Bareilles had finished and the crowd was waiting for Sugarland to take the stage. They said 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.

The wind that toppled the rigging came just minutes after that announcement, fans said.

"It was like it was in slow motion," concert-goer Amy Weathers told the Indianapolis Star. "You couldn't believe it was actually happening."

Associated Press photographer Darron Cummings was in the audience attending the concert as a fan shortly before the collapse. He said he and his companions sought shelter in a nearby barn after seeing the weather radar and eyeing dark clouds approaching.

"Then we heard screams. We heard people just come running," Cummings told the AP. "When you see dark clouds like that if there's going to be bad weather, there's going to be mass chaos on leaving."

Witnesses told WTHR that some of the injured were in a VIP section in front of the stage known as the "Sugar Pit." The witnesses said the dirt, dust, rain and wind came up the main thoroughfare of the fairgrounds just before the collapse.

"Panic kicked in when they seen the dust bowl coming in from the Midway," concert-goer Darryl Cox told the television station.

Another person at the concert, Emily Davis, told the station that there was lightning and the sky had gotten dark but it wasn't raining when the wind suddenly toppled the rigging.

"It was horrible, people were running and going crazy," she said.

Jessica Alsman told the AP the towering, metal stage scaffolding "kind of wobbled at first." Then pandemonium set in as it fell.

"As soon as we saw the wind gust, the wind was in our faces," Alsman said. She said and three friends grabbed each other and formed a chain.

"You can't imagine - we just thought it was going to rain or something," Alsman said.

Sugarland tweeted about the incident about an hour after it happened.

"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," the band said.

Indiana's position in the Midwest has long made it prone to volatile changes in weather. But even Wishard Memorial Hospital's spokesman, Harper, said he was surprised how things blew up without warning.

"I was at home watching a movie and I looked outside and all of a sudden the wind picked up. It had been a beautiful day up until then and then it started raining - and then I started getting calls on the pager."

In April 2006, tornado-force winds hit Indianapolis just after thousands of people left a free outdoor concert by John Mellencamp held as part of the NCAA men's Final Four basketball tournament.

And in May 2004, a tornado touched down south of the Indianapolis Motor Speedway, delaying the start of the Indianapolis 500 and forcing a nearly two-hour interruption in the race.

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Associated Press writer Caitlin R. King in Nashville, Tenn., contributed to this report.