A annual outdoor concert festival in Ottawa came to an abrupt and dramatic end when a sudden and violent storm swept through the riverside site, causing the main stage to collapse and sending thousands of spectators scrambling for shelter – including musicians and Mayor Jim Watson.

Eyewitnesses attending Ottawa’s Bluesfest Sunday evening say the first sign of the approaching storm came when cold air suddenly replaced the hot, muggy weather. Around 7:30 p.m., black clouds, lightning and driving rain followed, and a wind so strong that it folded the stage up in a manner of seconds.

The band Cheap Trick was on stage, singing their hit I Want You to Want Me when the storm clouds approached. The band posted a message on its Facebook.com site later in the evening. "Everyone is shaken up but band and crew are all fine," it states, "Cheap Trick hopes that everyone who attended the show is also ok."

The mayor had been on stage before their set, handing out awards.

“Suddenly the wind whipped up from the west and the storm rolled in. It was a scary moment, said Globe and Mail editor Ryan MacDonald, who was at the concert. “People started screaming and crying. The stage was a rectangle and it had scaffolding, three, four storeys high. The wind caught it and blew it backwards. It collapsed like a big tent. It was kind of unreal.”

Environment Canada had a thunderstorm warning in effect for Ottawa, saying winds were expected to reach 90 kilometres an hour.

Emergency crews who rushed to the scene combed the stage site for victims, but found none. Ottawa Fire Services spokesman Marc Messier confirmed that “at least two” people were transported to hospital with injuries by the time fire services arrived within a few minutes of the stage's collapse. He couldn't confirm the nature of their injuries, or whether anyone else was seriously hurt.

“One was a crew member, I know that one for sure,” he said.

“When we got there, we did a complete search of the exterior and underneath the stage and we were able to confirm there was nobody trapped.”

Concert organizers also issued a statement saying there were no serious injuries.

Another spectator at the concert who was about 200 feet from the stage when it collapsed said chaos followed in the minutes after.

“There were thousands of people running. The rain was pounding, pouring down sideways. It was insane,” said Globe and Mail reporter Jeremy Torobin. Moments before it collapsed, the main stage began to rock, he said, and then it fell in a matter of seconds. People scattered quickly and became bunched up near the exits as they tried to flee, he said.

internet site reference: theglobeandmail.com