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 4pm local time at Downsview Park, about five 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 cancelled 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 Labour 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 tweeted that "due to unforeseen circumstances tonight's concert at downsview park tonight has been canceled. Fans are advised not to make their way to the venue."

Radiohead's website had listed the concert as being sold out, with 40 000 tickets sold.

Jaime Rivest, 33, said at around 4pm the stage suddenly came down, crumpling and falling onto itself.

"It was like a tornado hit the stage and in just moments the stage came down with metal everywhere," she said.

Rivest said security officials rushed to evacuate the area. She said there was possibly about 1 000 people there hours before Radiohead was to take the stage at 9:30pm. The doors for the show opened at 5pm and other acts were scheduled to perform.

Police said the park wasn't full, but there was a considerable crowd of people already waiting for the show amid sunny and clear conditions.

Viljakainen said the Ministry of Labor would investigate to determine the cause of the collapse.

This is the second time Radiohead have to cancel a show in Toronto.

The last time was in 2003 due to a power outage when Radiohead were scheduled to play at Molson Amphitheater. At the rescheduled show at Toronto’s Skydome, which was also the last show of their North American tour, Thom Yorke stopped in the middle of Myxomatosis when a fan passed out. The band quickly resumed.

The 2003 show was rescheduled two months after. This time it might be harder. Radiohead are in the middle of their World Tour. The band move to Europe next, starting with a show in Rome on June 30th. At the moment, the band have no shows planned for August and September.

There have been a number of concert stage collapses in recent years.

In Canada, one person died and several people were injured when the stage went down at Bluesfest in Ottawa last July, and one person died and more than a dozen were injured in 2009 when a powerful windstorm caused the main stage to collapse at the Big Valley Jamboree near Camrose

Six people died last August when the stage collapsed at a Sugarland concert in Indianapolis; five died in Belgium when a storm swept in and toppled the stage at the Pukkelpop Festival.

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.