Police say at around midnight, officers and firefighters responded to Hamden Village, at 188 Treadwell Street, on the report of a structure fire.
Officers later learned that the fire was burning on the exterior wall of a specific apartment.
Police say a Good Samaritan used a fire extinguisher and a bucket of water to smother the flames.
One person was treated on scene for smoke inhalation.
The fire is now under investigation by the Hamden Fire Marshal and the Hamden Police Department Crime Scene Unit.