A sudden violent gale toppled the main stage at Ottawa Bluesfest in the middle of a Cheap Trick concert Sunday, sending thousands of people scurrying for cover as scaffolding buckled and tumbled onto electronic equipment.
At least two people were sent to hospital with minor injuries.
Eyewitnesses said band members were tossed off their feet when the storm struck shortly before 8 p.m., but Cheap Trick posted a statement on their Facebook page to say they were shaken but unscathed.
"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 showed the stage - which stood several storeys tall - being propelled backward before crumpling. Twisted shards of metal jutted out from the stage before it was destroyed.
Jordan Potechin, who was just outside the fence surrounding the site of the festival when the storm hit, said he saw the main stage topple over.
At that point, he said, the rain had not started, but there were a couple of flashes of lightning.
"The rain happened after I saw the stage collapse. It was more just wind.
"And as we were leaving the rain started."
The Bluesfest venue is almost the size of a football field.
"When we were walking away from it all we could hear were sirens, coming from every direction, fire trucks, police."
Another fan said he was just walking away from the main stage when the storm hit.
Michael Robert, 29, said he was about 50 to 70 feet away when he turned and saw the stage "start to buckle and just sort of folded in on itself and collapse."
"The whole thing just came down in a few seconds."
Bluesfest issued a statement saying that "due to extreme weather conditions, we have regrettably had to shut down all stages for the night."
A deadly storm shut down a a country music festival in Camrose, Alta., in July, 2009. Actor Kevin Costner and his band Modern West were just going on stage at the Big Valley Jamboree when the storm hit.
The stage collapsed, killing one woman and injuring 75 people.
An official with Bluesfest, who did not want to be identified, said the situation was chaotic in the moments following the stage's collapse.
But Robert said the fans didn't seem to panic.
"It was fairly orderly. People were aware that something serious was going on."
"There wasn't any pushing or shoving."
The windstorm caused major power outages across the Ottawa region.
Police said they received more that 300 emergency calls in a two-hour period, in addition to those from Bluesfest.
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.