The rock band Cheap Trick was performing at the Cisco Ottawa Blues Festival when a severe thunderstorm roared in.
Winds of up to 60 mph caused the stage to buckle and collapse. The musicians were thrown off their feet but were not seriously hurt. At least five people were injured, one seriously.
"Cheap trick was in the middle of their set and the stage just started to fall backwards and it fell pretty slow so hopefully everybody got out of there, but I've never seen anything quite like that before. It was pretty freaky," said a concert goer.
One person was gored by a piece of the collapsing stage. Members of the band said they're lucky to be alive.
The festival's executive director Mark Monahann said the stage was rented from a Montreal firm and was inspected regularly during the festival. The Ministry of Labour is surveying the site and will produce a report on the accident.
luesfest is one of North America's biggest 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 most celebrated international talent.
The Associated Press contributed to this report.