Kevin Richardson, a member of the Backstreet Boys who were slated to play Saturday night at Winstar World Casino in Thackerville, Okla. tweeted around 6:30 that a tent collapsed and some people seeking shelter there were injured.
Witnesses say a metal structure was blown over during the storms coming into south Oklahoma and fell onto people waiting in line to enter the venue.
Everyone who was injured was treated at the scene, according to reports.
Officials say they had seen the storm coming and warned concertgoers to take cover.
Kym Koch Thompson, a spokesperson for the WinStar World Casino and Resort, released the following statement: 'At 5:00 p.m., our officials began evacuating the outdoor concert venue after observing that lightning was within 4 miles of the casino.
'All patrons in the area were asked to move and to seek shelter from the storm.
All of the people injured were taken to hospital. Two individuals have since been released, the company said, adding that officers from the Lighthorse Police and the Oklahoma Highway Patrol, as well as Love County emergency responders, responded to the scene.
Backstreet Boy Nick Carter had tweeted earlier they are "waiting and praying for our fans that were injured". If we can perform were ready to go.
The official 98 Degrees account also issued an apology on Twitter, saying, "We are disappointed that tonight's show was cancelled due to inclement weather. Keep your tickets because, Backstreet WILL BE BACK", Richardson wrote. The most important thing is for everyone to get home safely and we will see you all very soon!'
The Backstreet Boys, often referred to as BSB, formed in 1993 and rose to fame in the late 90s.