The Union of Canadian Correctional Officers confirmed to CBC News that the incident happened at about 2 p.m. CT, with two separate fights breaking out in a hallway and in a living area.
Seven inmates have been taken to hospital to date, with five suffering stab wounds and two suffering blunt-force trauma, said union spokesperson James Bloomfield.
There is no word on the conditions of the injured inmates.
RCMP would only confirm that officers were called to the prison at 1:56 p.m. and were still at the scene as of 5 p.m.
Bloomfield said given the fights happened in separate areas, the union believes the attacks may have been planned. He said the drug trade may have fuelled the incident.