A man from Gosport has been arrested following a fire at a residential property in Jervis Drive.
Hampshire Police believe the incident took place between 9pm and 12am in a first floor flat on Wednesday.
A woman in her 50s, a man and woman in their 20s and a four-year-old girl were in the address at the time. They all managed to escape from a window.
All four are believed to have suffered smoke inhalation. The four-year-old was taken to Queen Alexander Hospital as a precaution.
A 28-year-old man has been arrested on suspicion of arson with intent to endanger life.
Police are now investigating into what happened and are appealing for witnesses.
If you think you have any information, please call 101 quoting reference 44180400893. Alternatively, call Crimestoppers on 0800 555 111, quoting the same reference.