It is too early to say whether a Horowhenua fire that killed a 22-year-old woman and a three-year-old girl overnight is suspicious, police say.

Firefighters were called to the house on Hulke Street, Foxton, 39km southwest of Palmerston North, about 2.15am, and extinguished the blaze by 3.30am.

On arrival, they began a search after being told there were people in the house and located the woman and child in the front bedroom of the single-storey wooden house, Manawatu assistant area fire commander Rodger Calder said.

"They removed them from the house and administered first aid, but unfortunately they were too late.

"It's really sad and the guys are pretty cut up about it. When you work that hard, work your butts off and have that outcome it's not a good feeling."

Detective Senior Sergeant Marc Hercock said another woman who was rescued from the house by neighbours was believed to be related to the child.

He said it was not clear what the cause of the fire was and that a scene examination was likely to continue for some hours.

"It is far too early to know whether the fire is suspicious or not, but there have been two deaths so it is natural for the police to become involved in order to report to the coroner."

Foxton chief fire officer Gary Stratford said it had been a rough night for everyone involved.

"We virtually knocked out the side (of the house) so entry could be gained and then basically discovered them."

Mr Calder said it was not clear what the cause of the fire was and fire safety inspectors were investigating.

"We're unsure if smoke alarms were in the house so we'll be following that up," he said.

Foxton Community Board chairman Basil Vertongen said the town would be devastated by the tragedy.

"It's a very sad sort of thing for a small community to lose two people," he said.

"In that street, everybody would know one another."

Mr Vertongen said the community had not lost anyone in a fire for a very long time.