A tragic incident is under investigation in Macassar Heights, where a 15-year-old girl and her 70-year-old grandmother were found unresponsive in their home on Tuesday morning.

Police say the pair were discovered in a bedroom in Allium Street just before 7 am and were declared dead on the scene.

An inquest docket has been opened, with a post-mortem set to determine the exact cause of death.

While investigations are ongoing, the deaths are suspected to be linked to carbon monoxide poisoning, possibly from indoor use of a coal brazier during cold weather.

Authorities have repeatedly warned about the dangers of using open flames or coals inside poorly ventilated spaces, as the gas produced is odourless and can be fatal within minutes.

The incident has left the Macassar community in shock, with the teenager believed to be a learner at a local high school.