TORONTO (Reuters) - A concert by the British rock band Radiohead was canceled after the roof of an outdoor stage collapsed during sound checks and rehearsals before the show on Saturday, killing one person and injuring three others, police and fire officials said.

Radiohead was not on stage at the time, police said, and a spokeswoman for the band confirmed that no member of the group was hurt in the accident, which occurred at about 4 p.m. local time at Downsview Park, about 5 miles north of downtown Toronto.

A Canadian musician named Dan Snaith, who performs under the name Caribou, had been set to open for Radiohead on Saturday, according to his website, but there was no immediate word on whether he was near the stage when the mishap occurred.

Representatives for the sold-out concert's promotion company, Live Nation, declined to comment. Downsview Park officials had no comment on the incident except to confirm that the Radiohead concert had been canceled as a result.

Toronto police spokesman Sergeant Tim Burrows told Reuters that about 20 people were in the direct vicinity of the stage, conducting rehearsals and sound checks, when it gave way.

A police statement issued on Twitter said one man in his 30s was pronounced dead at the scene and a 45-year-old man was taken to a local hospital with a non-life-threatening head injury. It said two other males were treated on the scene for less serious injuries.

Burrows said investigators were still unsure what caused the mishap, which was under investigation by the Ontario Ministry of Labor and the Toronto police.

"The roof part of the stage collapsed," Toronto Fire Services spokesman Captain Mike Strapko told Reuters.

"It's like an arch made out of round piping similar to what they use for scaffolding," he said, adding that the structure was rigged with lighting and other equipment. "So that's what came down and did crush the one individual."

Laura Eldeiry, a band spokeswoman, said Toronto was Radiohead's last stop on its North American tour.

Pictures of the scene posted on social media sites showed a large section of twisted metal scaffolding over and around the stage that had collapsed in the middle of the concert platform.

Radiohead, an alternative rock group led by singer Thom Yorke and famed for such hits as "Creep" and "Paranoid Android," is scheduled to go on tour in Europe this summer.

Their 1997 album "OK Computer" established the band as one of the top musical acts of the decade. The group made waves with its 2007 collection "In Rainbows," which the band ambitiously released first as a digital download while allowing customers to set their own price for it.