(CNN) At least 14 people were sent to the hospital Saturday after a storm knocked over concert entrance trusses at an Oklahoma outdoor concert venue hosting the Backstreet Boys and 98 Degrees, a spokeswoman for the property owner said.

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.

But about 150 people in line "did not heed staff's warnings."

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.

Read More