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Fire and Emergency NZ assistant area commander Mike Bowden said it is believed four children and the father were inside the property when the fire started on Tuesday night.
Three survivors have been confirmed - the father and two children.
According to a Givealittle page, a man - only identified as Des - heroically saved the lives of two young children and suffered injuries himself after re-entering the burning house in an attempt to save nine-month-old Arianna and the eight-year-old Brayden.
Brayden was rescued by firefighters during search and rescue operations, but later passed away.
The baby, Arianna, was discovered deceased in an "unsurvivable bedroom".
Bowden said she had been in the room where the fire was most intense, and her older sibling who died was found in the doorway outside this room.
He said the house had smoke alarms, which helped the father and two other children survive.
The Givelittle page has been created on behalf of the family. Christchurch-based charity NZ Gift of Love and Strength is also taking donations for the family, which can be dropped off at Little Explorers Preschool on Vivian St.
Neighbour Eddie Rodden described the fire as "chaos, really".
He said he woke to noise and the smell of smoke, and he looked outside to see two ambulances and police.
He has seen the family on his street before. He does not know them but described the children as "lovely".
Fire and Emergency southern fire shift manager Jill Higgison said emergency services received multiple calls about the fire on Vivian St just before 10.45pm.
Three fire crews arrived to find the single-storey home ablaze.
Another neighbour, whose house backs onto the damaged property, said he heard screams and cracking from flames at 10.30pm.
He quickly rushed out of bed and grabbed his garden hose, pointing it towards the burning house.
The neighbour said he heard screams from a male and children.
He said he saw a fire crew carry a young boy out of the damaged house last night.
Another Vivian St resident told NZME screams could be heard last night.The unnamed neighbour said it was just "devastating".
"We just heard screaming and then just all the flames, we just tried to get the hose out to try and help."
A St John spokesman said two ambulances and two rapid response crews were called to the burning home.
Two people were treated at the scene and taken to Christchurch Hospital.
One fire crew remained at the scene overnight to monitor hot spots.
A scene guard was in place on Wednesday and part of Vivian St was blocked off.
- By Matt Slaughter, additional reporting NZ Herald and RNZ