The staff at the venue had begun evacuating fans after lightning was spotted, Kym Koch Thompson, a spokeswoman for WinStar World Casino and Resort, said.
Thompson said the area was pounded by heavy rain and winds as strong as 80 mph.
Prior to the incident, Backstreet Boy Kevin Richardson tweeted that the bands were expecting a sold-out concert with about 12,000 attendees. Richardson later tweeted that the concert had been canceled because of the storm and injuries to fans.
Linda Tesfatsion was waiting for the concert to start at the venue in Thackerville when the storm went through, she said.
“Hundreds of Backstreet Boys fans playing chicken with an Oklahoma storm right now. Giant metal entrance structure, portable toilets, blew over. A handful of people left in ambulances,” she wrote on Twitter with a picture of the structure that fell.
She said she saw four people put on gurneys and taken away by ambulances. A few of the injured had bandages on their heads but were able to walk, she said.
The metal structure that fell was holding up a purple banner that read “The Colosseum at WinStar,” she said.
Two of the people who were hospitalized have been released, Thompson said Saturday night.
“We never want to put our fans in harm’s way and with tonight’s weather and the injuries from earlier, we have decided to cancel the show and will attempt to reschedule. The most important thing is for everyone to get home safely and we will see you all very soon!”
Richardson tweeted, “unfortunately, due to damage sustained in the storm earlier this evening, we are unable to perform the show tonight. Safety is always #1. Keep your tickets because, Backstreet WILL BE BACK!”
Members of the band 98 Degrees tweeted they were disappointed that Saturday’s show was canceled due to the weather.
“We know many of you traveled to be here today. Sending you all our love and hope to see you soon.”
CNN’s Nicole Chavez contributed to this report.
News credit : Cnn