A 60-year-old man managed to escape the blaze in the fifth floor unit, but was left in intensive care, while his wife, 47, two daughters aged 26 and 27, and granddaughter, 2, died either at the scene or in hospital.
A 90-year-old man living on the 10th floor of the building was also taken to hospital after inhaling smoke.
In a media briefing, chief inspector Ma Ling-ho said an initial investigation suggested that a lithium battery in a massage chair overheated and caught fire, and that the blaze then spread quickly.
But in a statement later, police clarified that an overheated battery might have sparked the fire, without specifying whether if it was a lithium battery or belonged to the massage chair.
Nine fire engines, seven ambulances, and 93 emergency personnel were deployed to the fire at Po Tat Estate.
The blaze, which forced almost 200 people to flee their homes, was put out after around an hour.
Last updated: 2021-04-16 HKT 20:13