A neighbor said the burnt down unit is about 600 to 700 square feet, and a mother and son had lived there for some 30 years. The son worked as a night security guard in North Point, while his mother was a member of the Owners' Corporation.

It was understood that the son was smoking in the room at the time of the incident, and the blaze is suspected to be caused by bedding that was ignited by cigar ash.

The flat concerned was still cordoned by police on Monday morning. The power supply of the floor corridor has not yet been restored, and three elevators in the building are out of service.

The fire broke out at 5.47pm on Sunday at a flat on the eighth floor of Yip Cheung Building, Hill Road, Shek Tong Tsui. At least two men and three women were injured by smoke inhalation and sent to Queen Mary Hospital. Some 100 residents had to be evacuated to the ground floor and rooftop.