Police and fire investigators have completed a scene examination but have still not revealed what sparked the early morning house inferno that killed a Christchurch teen at the weekend.

An investigation, as well as a post-mortem examination, indicate that 16-year old Corey James McLean was likely to have been asleep in a back room of the Medina Crescent property before the fire started and has not woken up.

He had been hailed a hero in the initial accounts to come out of the tragedy.

Neighbours reported the youngster trying to save Sayler Hutchinson-Clarke -- a young mother expecting her second child -- from the blaze in the Parklands area of the city.

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But police have told Ms Hutchinson-Clarke and the property's Housing New Zealand Corporation (HNZ) tenant, Wendy Marsh, that the teen had been found dead in the bed where he was sleeping that night.

Ms Marsh lived at the house with her three teenage children, Rikki, Mikayla and Cheyanne Marsh.

Four others, including Corey and Ms Hutchinson-Clarke, had stayed the night.

Marsh family spokeswoman Piwi Beard, 53, said reports the teenager had died saving Ms Hutchinson-Clarke were "very upsetting" for her.

While the scene examination is complete, investigations into the cause of the fire are ongoing.

"Indications are that the fire was extremely intense and the other occupants were very lucky to have got out," a police statement said today.

The Fire Service has today confirmed that smoke alarms were fitted at the property and were checked in June this year by Housing New Zealand.

However, police said: "[Fire Service] cannot confirm at this stage whether the smoke alarms were working or not at the time of the fire."

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Victim Support are working with the families.

Both police and the Fire Service say the tragedy is "a timely reminder of the need to have working smoke alarms fitted and an escape plan as fire moves incredibly fast".

Overcrowding concerns at the house have also emerged but been denied by Ms Marsh.

There were four names on the tenancy agreement, but HNZ said it had recently become aware there "may have been other people living at the property".

"However, we had not had an opportunity to contact the tenant to discuss the situation prior to the fire," a HNZ spokesman said yesterday.

Work and Income staff met Ms Marsh yesterday, with the Ministry of Social Development agreeing to provide some emergency assistance to cover her accommodation costs for this week.

"We'll continue to stay in touch to see if there's other support we can provide as housing providers look to find her another property. We're here to help in any way we can," ministry regional director Annie Aranui said.