The "distressing incident" occurred on the morning of Friday, August 5, when paramedics called for assistance in tending to the "seriously ill young person" who suffered a cardiac arrest.

It is unclear whether the teenager suffered cardiac arrest at the property or in an ambulance on the way to the hospital.

It is common for fire crews to assist paramedics in such circumstances, but sources told The Canberra Times that fire crews would not enter the property when they were told there were COVID-positive people inside.

Instead, paramedics had to call for another ambulance.

A police spokesperson confirmed the investigation into the death, but declined to comment further while the investigation is ongoing.

"ACT Policing can confirm it is investigating the death of a 13-year-old child on behalf of the ACT coroner," they said.

The ACT Emergency Services Agency has also begun a review into the response.

ACT fire crews are required to wear full personal protective equipment, including a N95 mask, when assisting ambulance crews.

They are also told to undertake a risk assessment before entering a property.

United Firefighters Union ACT branch secretary Greg McConville has previously said he was confident the fire crew members will be exonerated by the investigation.

"While the matter is investigated firefighters are unable to defend themselves publicly, and this results in gross unfairness to both them as individuals and to the ACT Fire and Rescue service as a whole," he said.

"I am confident that a due process of inquiry and an objective assessment of the facts will see our members exonerated."