Police are treating the death of a woman who died in a Hamilton house fire overnight on Tuesday as a homicide.

The woman, who is believed to be Wai Tangi Matenga, 37, was one of nine people at the Holland Rd house when the fire occurred.

Detective Senior Sergeant Nigel Keall of the Waikato CIB said there was about 30 police staff working on the unexplained sudden death enquiry.

"In addition to our staff we are being assisted by ESR forensic experts and Fire Service investigators as we commence our scene examination today,'' Keall said.

"Owing to hot spots reigniting in the house yesterday we were unable to conduct more that an initial reconnaissance of the scene and a priority for today will be commencing the scene examination, hopefully to the point where we can remove the victim's body to allow a post-mortem examination to be carried out in Auckland tomorrow.''

Meanwhile, police were praising the efforts of another occupant of the house, who helped to rescue two preschoolers from the burning house.

It is understood Matenga lived with her two teenage children and two other children, aged 1 and 4, who were understood to be the children of her younger sister, who died about three months ago from a medical condition.

''We know that one man managed to pull a four-year-old child from a lounge window and then re-entered the house to successfully rescue the baby.

''Had it not been for this person's actions we would be investigating a far greater tragedy.''

Keall said investigations of this type were evidentially based and the considerable damage to the interior of the house and resulting water damage caused during the battle to control the blaze means investigators will have to manage a number of time consuming challenges.

"To that end we are keeping foremost in our minds that we are working on behalf of the victim and that person's family."

- © Fairfax NZ News