A young mother desperately called for help before smoke from her burning home killed her and left her two children seriously ill.

Neighbours broke into the Paraparaumu Beach home early yesterday by smashing through Roselle Ramirez's bedroom window - but it was too late to save Miss Ramirez, who was trapped inside with her children Jordan, 7, and Reyna, 5.

The 25-year-old died at the scene and the children are being treated at Auckland's Starship hospital for smoke inhalation. They were in a serious but stable condition last night.

Flatmate LeahMay Mijares Osik escaped the inferno unharmed with her son and another adult. She told the Herald Miss Ramirez was a "wonderful mother" who would not have left her children.

"That's why they would have been trapped ... she wouldn't have left them for anything."

Speaking outside the Callender Tce house yesterday, Miss Mijares Osik recalled trying to get to her flatmate when the fire started about 12.30am.

"I saw [a] big fire so I went to Roselle's room because she had a little window and yelled 'our house is on fire' ... We tried opening the window and the last thing I heard was her saying, 'What the hell is going on? Help us."'

Soon after, Miss Ramirez stopped talking. When her flatmate went inside she was confronted with smoke so thick she could not breathe.

"I shut the door and went outside and got the hose from out back thinking it would reach her room but it didn't - it didn't do anything."

Neighbours alerted by the flames gathered outside, Two men smashed the bedroom window and pulled the children and their mother out. It is believed one of the children was found in a cupboard.

The search seemed to take forever. "I was like 'what's taking so long'," Miss Mijares Osik said.

There was no working smoke alarm in the house because the battery had run flat the night before. When it started beeping in the afternoon, indicating low battery, Miss Ramirez "went in there and took the battery", Miss Mijares Osik said.

"I thought she put it back but obviously she didn't otherwise we would have heard the alarm. Who would have thought we would have had a fire that night. We didn't know."

Miss Mijares Osik only moved into the house six weeks ago but has known the mother for several years. They originally met in the Philippines but became closer when Miss Ramirez moved to New Zealand in 2003.

Neighbour Stacey O'Brien, 31, saw Miss Ramirez and one of the children carried out of the house. She said ambulance officers took the children away immediately but worked furiously to try and revive their mother.

Police and fire safety officers completed their examination of the house late yesterday afternoon.

Senior Sergeant Alasdair Macmillan of the Kapiti police said the fire could have started with a laptop.

"We believe the blaze started in the vicinity of a laptop, which was in the corner of the lounge room and was charging at the time."