The main stage at Ottawa's Bluesfest collapsed Sunday night under a severe thunderstorm, injuring several people, one severely.

Ottawa paramedics said one person was rushed to hospital with "life-threatening injuries" and another person was "severely injured."

The patient with life-threatening injuries was taken to hospital with a piercing wound to the abdomen and a fractured leg and pelvis, paramedics said.

It is believed part of the stage broke off, piercing the man's stomach, CTV Ottawa's Graham Richardson reported.

At least three people were taken to hospital. Others were treated for minor injuries.

Earlier, the festival's Twitter account announced there were no "serious injuries."

There are multiple emergency vehicles on site.

Ottawa Fire Services said that a second search under the collapsed stage confirmed that no one was trapped underneath.

Classic rock act Cheap Trick had been performing for about 20 minutes at the time of the collapse.

The band left the stage just prior to the collapse.

"Everyone is okay and we are so lucky to be alive and hope that all the fans are okay too," the band said in a message on Facebook.

Jordan Potechin said he saw the stage topple over, after several flashes of lightning but before the rain started coming down.

"The rain happened after I saw the stage collapse. It was more just wind," he told The Canadian Press.

"And as we were leaving the rain started."

Thousands of concertgoers took shelter in the nearby Canadian War Museum, according to reports.

Environment Canada warned that winds could reach up to 90 kilometres per hour in Ottawa Sunday night.

Fire officials said there were numerous reports of downed wires and trees in the Ottawa area.

Bluesfest cancelled the remaining performances Sunday night, including headliner Death Cab for Cutie.

The festival, which first took place in 1994, has grown into one of North America's major summer music events.