Wong Shue-kwung, 26, and Kan Ho-kin, 13, are believed to have been poisoned by carbon monoxide from the heater. The windows in the flat were closed.

The Gas Safety Advisory Committee heard five other similar deaths had occurred due to the same heaters since 1991 when legislation was introduced banning their installation.

Acting committee chairman Leung Cham-tim said the incidents showed the legislation needed strengthening. Users were ignoring safety warnings, such as ensuring ample fresh air.

Mr Leung said the heater involved in the Shekkipmei incident was up to safety standards for those requiring fresh air from outside a flat.

'But the room was previously a balcony which had been sealed without authority after the heater's installation,' Mr Leung said.

'So an appliance which was actually safe at the time of installation resulted in unsafe consequences. This is why the legislation needs to be amended.' Chief Electrical and Mechanical Services Department engineer Fu Tai-pun said some owners were reluctant to upgrade heaters despite warnings of the risks.

'This [law change] is likely the most effective means of totally removing the risk [as it will] eliminate the dangers of tenants enclosing balconies, blocking ventilation openings and missing safety inspections,' Mr Fu said.

Towngas is offering those replacing the heaters up to a 40 per cent discount on new heaters which cost up to $3,600. It also is offering other incentives, such as 10-month, interest-free payments.

The committee suggested implementing the amendment with a six-month grace period to allow users time to replace heaters. It also would ensure their fitting before the following winter.

The amendments will be recommended to government officials before going to legislators for final approval.