Toronto Police say a man in his thirties is dead after the stage at Downsview Park collapsed late Saturday afternoon, hours ahead of a scheduled concert by rock band Radiohead.

Toronto Police Const. Tony Vella told reporters that "a number of people" were on the stage preparing for the concert when the top portion collapsed. While a number of workers fled to safety, four others were caught in the wreckage.

Toronto Fire platoon chief Tony Bellavance said firefighters had to extricate one person, who suffered crushing injuries and was pronounced dead at the scene.

Police also said a 45-year-old man was taken to Sunnybrook hospital with a non-life-threatening head injury after the incident, which happened around 4 p.m. ET.

Two other males were injured, but were treated at the scene by paramedics.

Toronto Fire Services and contractors secured what was left of the large stage, so a full investigation could safely begin.

"One thing that we're going to be doing is working closely with the Ministry of Labour, trying to determine exactly how that stage came down," Vella told reporters during an evening news conference.

Vella urged witnesses to contact police.

The stage collapsed hours before Radiohead was set to perform to an audience of 40,000 people. Not long after the incident, officials from Downsview Park confirmed that the sold-out concert had been cancelled.

Ticketmaster posted a message to its website saying that all tickets will be refunded at point of purchase. Concertgoers who bought their tickets online or by phone will receive an automatic refund. Those who bought their tickets at a retail location can return them to the same location.

A number of concertgoers were already at the park when the stage collapsed and were evacuated from the area.

Aerial pictures from the scene showed the pipes that made up the roof of the stage lying in a heap on top of the stage itself.

Chris Collins arrived at the park for the concert just before the incident unfolded.

Collins said he heard a "prolonged crashing noise that was sustained for probably five or 10 seconds."

He looked up to see that "the whole structure kind of imploded through the middle."

A moment later, Collins said, event staff began running toward the stage area. Paramedics arrived on the scene shortly after.

The stage was set up in the north-west corner of the large park, which is located in the north end of the city. The popular urban park hosts a number of large concerts and performances every year.

The Ministry of Labour has been called in to investigate.

The incident follows a number of similar deadly mishaps in recent years. Last August, six people were killed in Indianapolis when a stage collapsed at a Sugarland concert. In Belgium, five people were killed when a storm knocked over the stage at the Pukkelpop Festival.

In Canada, several people were injured last July when the stage collapsed at the Ottawa Bluesfest. In 2009, a windstorm swept through Camrose, Alta. during the Big Valley Jamboree, killing one person and injuring more than a dozen others.

With files from The Canadian Press