Fire crews from St Mary’s and Hightown were called to the scene of a fire on Portswood Road shortly after 9am on Wednesday, April 29.
The fire was quickly extinguished using hose reels, and the property was ventilated to clear smoke.
Portswood Road was closed by emergency services between the junctions of Bowden Lane and Mayfield Road while they attended the scene.
Firefighters left the scene and returned to their stations by 9.45am, and the road was opened just before 10.30 am.
A spokesman for Hampshire and Isle of Wight Fire and Rescue Service said: “Smoking remains one of the leading causes of fatal house fires.
“Taking simple precautions can save lives.”
The service advises people to always fully extinguish cigarettes and dispose of them safely, use deep, sturdy ashtrays away from soft furnishings, and avoid smoking in bed or when feeling drowsy.
A spokesperson for Hampshire police said the fire was not believed to be suspicious.