About 100 people evacuated a residential building at 4-6 Dung Fat Street in Tsuen Wan after smoke emerged from a stairwell shortly after midnight on October 1.
The smoke was reported at about 00:42. Responders found renovation materials burning in the stairwell and firefighters extinguished the blaze.
A 32-year-old male resident felt unwell after suspected smoke inhalation and was conscious when he was taken by ambulance to Yan Chai Hospital.
Personnel at the scene found a suspected accelerant. Police provisionally classified the case as arson, and no arrest had been made at the time of the reports.