At least five people were injured, one seriously.
Cheap Trick's band members got off the stage safely, but witnesses said they were thrown off their feet. "Everyone is okay and we are so lucky to be alive and hope that all the fans are okay too," the band, best known for hits including "Surrender", "I Want You to Want Me" and "The Flame", said in a message posted on Facebook.
Video of the Bluesfest site posted on YouTube within minutes of the storm's passing showed a stage that had crumpled and collapsed over electronic equipment. Twisted shards of metal jutted out from the stage, which stood several stories tall before it was destroyed.
Marc Messier, a spokesman for Ottawa Fire Services, said a 49-year-old man was in serious condition with abdominal, pelvic and leg injuries. Another had a spinal injury and a third person experienced chest pains.
At least eight other people were treated at the scene for minor issues including twisted ankles and anxiety.
Environment Canada had a thunderstorm warning in effect for Ottawa, saying winds were expected to reach 56 mph (90 kph). Bluesfest is one of North America's main musical events.
The festival first took place in 1994 and has since grown from a one-stage, three-day event to a multi-staged, 12-day music showcase featuring some of the best international talent.[/img][/COLOR]