Police were called to 224 St. Clarens Avenue at about 6 a.m. because of a fight. One man had been stabbed, another man involved in the fight was subdued by police with a Taser. He has also been taken to hospital.
One man's injuries are serious, according to paramedics.
The building is divided into rental units. A neighbour told CBC News the fight was preceded by one man yelling at the house from outside, after which there was a scuffle in the doorway.
Police from Toronto's 11 Division are investigating.