Toronto police said the knife was struck in a building on Markham Road and McNicoll Avenue shortly before 6:30 p.m.
When emergency crews arrived, they located two victims at the scene and later found a third a short distance away.
Toronto rescuers said all three were rushed to hospital – one in critical condition and one in serious condition. The third victim had minor injuries.
Police said a man was arrested at the scene and that there was no danger to public safety.
Police added that they were not looking for other suspects.
