One woman has been killed and 15 people have been injured after a powerful storm knocked down the main stage at the Big Valley Jamboree in Camrose, a small city near Edmonton.

The main stage collapsed just as American country singer Billy Currington was wrapping up his set.

Fifteen people have been taken to hospital and four people have been classified as "critically injured."

Camrose Police Chief Darrell Kambeitz told The Canadian Press that all of the injured have been taken to hospital and reports that dozens were trapped under debris are untrue.

"One individual is confirmed deceased and fifteen others were injured. All of the injured have been transported to hospitals. Decisions regarding the continuation of the jamboree will be made at a later time."

Country singer Jessie Farrell said she watched the stage collapse from her trailer and said it collapsed inwards like it was in an "explosion."

"The stage is in a million pieces," the Vancouver-based singer said.

She told CTV News Channel Saturday evening that there was about a minute warning of a storm coming, which she described as like "bombs going off."

"Lightning, hail, thunder . . . it looked like a tornado," she said. "Debris was flying everywhere."

"People were missing and trying to find each other and there was a woman who was trying to tell everyone to stop panicking and she was panicking on the speakers."

The storm has been described as having "hurricane" level winds and marble-sized hail.

Farrell said about 15,000 people were attending the show. The Jamboree is Canada's biggest country music festival.

On her Twitter account, she said Currington's face was bloodied but he appeared to be OK otherwise.

The accident occurred at about 6:00 p.m. local time.

Actor and country singer Kevin Costner was due to perform Saturday evening. Costner went to the hospital to comfort those who were hurt but was not injured himself.

Costner and his band Modern West were due to perform next before the accident.