A 34-year-old man was stabbed twice in the leg in an incident at a flat in Balfour Road, Kingsthorpe Hollow, sometime between 12.30pm and 1pm yesterday.
An air ambulance was called to the scene to airlift the victim to hospital, but his injuries were not thought to be life-threatening.
Police cars and a cordon lined the streets for 10 hours while investigators examined the scene, and a manhunt is now on for the attacker.
One nearby homeowner, who asked not to be named, said: "I didn't realise what happened until I looked out my window and saw the street was taped off. They were here about 10 hours."
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Detectives are seeking a man "in his early 20s" they want to speak to in connection with the attack.
The offender, who is believed to have run off in the direction of Bunting Road, was described as black, aged in his early 20s with a slim build. He had long black hair, possibly either in dreadlocks or matted, and he was wearing a dark-coloured hoody and dark jogging bottoms.
Anyone with information should call Northamptonshire Police on 101 or Crimestoppers, in confidence, on 0800 555111.