The executive director of the Ottawa Bluesfest says that all of the people taken for treatment in the aftermath of a Sunday night stage collapse have been discharged from hospital.

Mark Monahan spoke to reporters Monday, the morning after a sudden storm swept over the outdoor concert and toppled the main stage just after 8 p.m. Sunday.

Monahan said about 10,000 people were at LeBreton Flats Park at the time of the collapse, though he could not say how many were watching the performance by Cheap Trick who had been performing on stage.

A severe thunderstorm watch had been in effect on Sunday night, but CTV Ottawa reporter Katie Griffin said the storm arrived with little warning and caught everyone by surprise.

"It just happened so fast," Griffin told CTV's Canada AM from Ottawa on Monday morning.

"There was really nothing anybody could do."

When Monahan was speaking to reporters, he described the storm as a "freak" event that caused no other damage at the park.

"It was a very unusual situation," he said. "The fact that it brought that stage down and nothing else came down in the park was just a freak situation."

The collapse occurred on the final night of the festival. All performances were immediately cancelled after the stage collapsed.

"We were monitoring the weather and what was a watch turned into a more severe situation and when that happened we called it immediately," Monahan said.

In light of what happened on Sunday night, Monahan said the festival will "be looking at" closer liaison with the weather office in future.

The collapse at this year's Bluesfest is now under investigation by the Ministry of Labour.

The Cheap Trick website said that no one from the band was injured in the collapse, with band members wishing "that everyone who attended the show is also ok."

Cheap Trick were supposed to be one of the last bands to perform on the last night of the festival, with Washington's Death Cab for Cutie due to close out the show.

On Twitter, Death Cab bassist Nick Harmer described seeing the stage collapse, right before his own band was supposed to go on stage.

"I have never seen wind blow an entire stage flat. I'm in shock," Harmer tweeted Sunday night.

Harmer said Death Cab had "narrowly escaped disaster" by not being on stage when the storm hit.

Death Cab leader singer Benjamin Gibbard told his own Twitter followers that the band would return to Ottawa at a later date. He also expressed relief that no one died.

"It was a miracle no one was killed today when the stage collapsed," Gibbard said.

"Gear can be replaced, people can't."

With files from The Canadian Press