The school in La Loche was on lockdown, and Royal Canadian Mounted Police urged parents to stay away while they responded to the "ongoing serious incident."
A nearby elementary school was also shuttered and students kept indoors "as a precaution," a police spokes person told AFP.
Canada's public broadcaster said two people had died in the remote northern town and several patients were being treated for gunshot wounds, while other local media said a suspect had been arrested at the scene.
Police in the town of about 3,000 people, located about 600 kilometers (375 miles) north of Saskatoon, would not immediately confirm the reports.
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