(CNN) -- A massive gust of wind brought down a stage at the Indiana State Fair on Saturday night, killing at least four and injuring 24, officials said.
Authorities said they feared more casualties.
"A big gust of wind came through. You could see a lot of people panicking. All the scaffolding and speakers -- all that came crashing down -- and the whole stand just collapsed," said Aaron Richman, who witnessed the collapse at the Indiana State Fairgrounds in Indianapolis.
The Indianapolis Department of Public Safety posted on its Twitter page the death toll and said that 24 people had been taken to area hospitals.
Two local hospitals placed the number of injured at 43, including some walk-in patients.
Capt. Brad Weaver, commander of special operations for the Indiana State Police, said he took the stage at 8:45 p.m. to warn the audience of severe weather.
Ten minutes later, the wind gust blew through.
He said he "saw the framework from the stage start to come over."
He said he and others took cover behind a trailer, which was also struck by debris from the stage.
Sara Bareilles had finished her set at the Hoosier Lottery Grandstand stage when the wind knocked down the rigging on to the stage.
"I'm speechless and feel so helpless," Bareilles said on her Twitter page. "My heart aches for the lives lost."
The show's headliners, country music duo Sugarland, was to take the stage next.
"We are stunned and heartbroken for the fans and their families in Indiana." said Sugarland singer Jennifer Nettles. "We hold those injured in our prayers at this very sad time. There are no words. It is tragic."
The official Twitter page of the Indiana State Fair said officials would make announcements "as they come."