A suspected arson occurred at 2am in a flat on the 19th floor of Fung Wai House.

Seven people were reported to be injured or suffered from smoke inhalation, of whom two -- a woman aged 76 and her grandson aged 28 -- were unconscious and sent to hospital in critical conditions.

In addition, a 74-year-old man, a seven year old girl and a six month old infant were sent to hospital for feeling unwell.

The 57-year-old suspected arsonist believed to be living alone on that floor was later arrested in the stairwell, from whom police officers seized two knives. The man was sent to hospital with burns on his back and burnt hair.

The fire was put out in about 50 minutes. About 400 residents were evacuated during the fire. The site was cordoned off until morning, and affected residents were seen waiting downstairs while the management office delivered supplies.

A neighbour of the arrested man said he moved in about 10 years ago and has three sons, two of which are in boarding schools and the youngest lives with the man's parents.

She said the family used to have social workers visit, but the workers normally only sit outside the gate to talk to the man and never enters the flat.

She added that the man's wife and youngest son moved out three years ago. After that he lived alone, and no social worker was seen coming over.

Another resident downstairs said he had often heard the man screaming for no reason.