He said the father recently started a new job, but he did not say whether the job change had any link to the accident.

He admitted the children sometimes played outside of the building on their own. 'They could open the home's door by themselves and play outside,' he said.

They were able to open the home's locked gate, he said.

The same family was rescued uninjured by fire officers after a blaze broke out in the kitchen of their home on a Sunday morning in January.

The father had fallen asleep and left a pot of water, with bottles of milk inside, heating on the gas stoves unattended. He was awakened by the dense smoke and he immediately took his son and daughter up to the building's roof, where they were rescued by firefighters.

Neighbours said that they often saw the children hanging around by themselves. Mrs Yau, a neighbour of the family who lives on the sixth floor, said that the children were often seen to be alone. 'The other day I saw him [the elder child] in the elevator, but he did not speak,' she said.

Amy Fan Yuk-shan, who has lived in the adjacent building for seven years, said that the neighbourhood was familiar with unattended children playing in front of the building.

'It [the situation] is quite well-known here,' she said. This section of Tseng Choi Street is lined with several independent residential buildings, and a small park in front of them.

Ms Fan urged the government to put more resources to what she called a 'forgotten area' in Tuen Mun.

Priscilla Lui Tsang Sun-kai, executive director of Against Child Abuse, said many parents had underestimated the risks of leaving unattended children at home and overestimated the children's abilities. 'It's heartbreaking to see that children are exposed to risks of permanent trauma and injuries, or even death, when their parents just leave them unattended for minutes,' she said.

In July, a two-year-old girl fell to her death from window when she was left alone at Shek Kip Mei home by her mother.