Initial estimates had put the number of injured at about 15.

The large stage crumbled on Saturday after heavy winds battered the audience at the Big Valley Jamboree, an outdoor festival in Camrose, about 100 kilometres southeast of Edmonton.

Two people caught in the collapse are in critical condition, according to a spokesperson for Panhandle Productions Ltd., the event organizer.

The stage fell apart just before Hollywood actor Kevin Costner was expected to perform with his band, Modern West.

His manager, Nick Meinama, said they were stuck underneath the stage but were not hurt.

"We wiggled our way out," Meinama told CTV News Channel on Sunday. "We found that our road manager and guitar player had been hurt, but the ambulance and the paramedics were here instantly to take them to the hospital."

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."

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