A family-of-three had to use buckets of bathwater to put out a fire blocking their escape route.
Police are treating the blaze, which broke out last night at the ground-floor flat in Woodend Crescent, Windhill, as suspicious.
Scenes of crime officers are investigating and said the seat of the fire was at the back of the front door.
No-one was hurt but paramedics attended after an emergency call at 11.30pm reported people trapped inside the flat.
A fire service spokesman said: "One of the adults had been running a bath at the time of the fire and luckily they were able to use buckets of it to put it out. There was quite a bit of smoke but they managed to put it out themselves. Scenes of crime were there last night. They're treating it as suspicious."
A police spokesman also confirmed the incident was under investigation.
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