The government should set up a database of at-risk elderly people, a lawmaker said on Friday, a day after a man in his 70s was found dead with his son unharmed beside him.

Police were alerted on Thursday when security personnel detected a foul odour coming from a flat at Butterfly Estate in Tuen Mun.

The force said officers discovered the body of the 78-year-old man.

His 44-year-old son, who is reportedly mentally challenged, was next to the elder.

On Friday, lawmaker Bill Tang said authorities should consolidate the data they have about the city's senior citizens, noting that government units like the Social Welfare Department and the Hospital Authority hold the majority of information about these individuals.

"The government can and has to integrate such database and form a high-risk elderly and family database, and facilitate the different kinds of social service organisations and community organisations... to care [for] and reach such kind of high-risk families," Tang told reporters.

One way to check up on such households would be to install sensors on devices around the flat, Tang said.

He said the sensor would be triggered and send an alert if the home's gate, for example, has not been touched for 48 hours.

Fellow legislator Stanley Li said the tragedy highlighted the need to shore up support for carers, adding the administration should offer more training for people to become caretakers.

The Social Welfare Department expressed concern about the incident, saying it has arranged for social workers to contact the family and provide assistance.

It is understood the family involved was not a case under the department.