A predawn blaze in a Kwun Tong flat yesterday that killed three members of a family of five may have been caused by overloaded power sockets.
Preliminary checks suggested it was an electrical fire, according to a police source close to the investigation.
Detectives were also looking into why the fire spread so fast and caused such heavy casualties. It was believed to have been extinguished within 30 minutes.
Chemists and officers from the Electrical and Mechanical Services and Fire Services departments have been called in to help the investigation.
Last night, the family's youngest member, eight-month-old Chan Hoi-yee, was in a critical condition at United Christian Hospital after being rescued unconscious from a bed she was sharing with her mother Lung Po-king, 33.
Lung died along with her two young sons, Chan Kai-lok, five, and Chan Kai-yin, two.
The retired policeman was treated for minor arm injuries and smoke inhalation, and discharged from hospital in the afternoon.
The blaze broke out in the living room of the 20th-floor flat in Tsui Lok House, Tsui Ping South Estate, at 3.08am as the family slept in two bedrooms.
"We were told Chan was woken by his wife and he went out to get a fire hose from the corridor," a second police source said.
"He was probably flustered and did not know how to operate it. As he returned, he could not re-enter the flat because the flames were so intense."
A male neighbour said that Chan appeared to be agitated. "He was pulling a hose in the corridor and asking his wife to open the windows.
"Dense smoke was billowing from the burning flat at the time and his wife was inside."
Police said autopsies would be conducted.
"The fire was probably caused by an overloaded plug extension used by a television, a TV set-top box and other appliances," the first source said.
"We suspect the extension burst into flames and then set the flat alight."
The flat was severely damaged, with all the walls and ceilings blackened, and furniture and electrical appliances ruined.
Police said about 500 residents were evacuated from the building.
Nine fire engines and five ambulances were deployed to the scene. The fire was extinguished at 3.29am - about 20 minutes after it started.
All suffered burns and were unconscious when found, acting Kowloon East fire divisional officer Pang Chun-yin said.
Lung and her two sons were declared dead at nearby United Christian Hospital.
Paramedics gave Hoi-yee a cardiac massage and held an oxygen pump to her face as she was being carried into the hospital's accident and emergency area.
"She's in a coma in the intensive care unit and in a life-threatening condition," the second source said yesterday evening.
Chung Chi-ming, chief inspector of the Kwun Tong district crime squad, said initial investigations found nothing suspicious, but investigators had collected all electronic equipment from the flat for checks.
A woman who said she had known the Chan family for about five years sobbed. "The family always smiled when they saw me," she said. "The baby is a beautiful girl and the family seemed very happy.
"I am so shocked. It is really sad."