A stage collapse hours before a Radiohead concert in Toronto was to begin on Saturday left one person dead and three injured, officials said.

Emergency Medical Services deputy commander David Viljakainen said a man in his mid-30s, who was trapped under the rubble, was pronounced dead at the scene.

A 45-year-old man was hospitalised with a head injury and two were treated at the scene, said Viljakainen.

The concert was cancelled.

Police spokesman Tony Vella said crew were setting up the stage when it collapsed.

"Unfortunately, four people were hurt. The remainder of the people, when they heard the stage coming down, ran from the area," Vella said.

Radiohead tweeted that "Due to unforeseen circumstances, tonight's concert at Downsview Park has been cancelled.

"Fans are advised not to make their way to the venue."

Jaime Rivest, 33, said: "It was like a tornado hit the stage and in just moments the stage came down with metal everywhere."