A woman found in the bedroom of a burning North Shore home died so violently it has prompted police to begin a murder investigation.

A team of 20 officers are now working on the case, and two fire safety investigators are sifting through charred debris at the badly damaged house to find out how the blaze began.

The woman, who had still not been publicly identified last night, was found dead on Saturday night when firefighters were called to the blazing house in View Rd, Glenfield.

Neighbours, some of whom tried to fight the blaze with garden hoses until firefighters arrived, reported seeing flames up to 5m high.

They did not realise anyone was inside because all of the lights were out and there were no cars in the driveway.

It was only when they heard someone crying out from the backyard that they discovered a man with extensive burns to his hands and realised a woman was still inside.

"He was just saying, 'I couldn't get to her, I couldn't get to her'," said neighbour Colin Preston. "He was just in his underpants. All his skin - from top to bottom and his face - was just covered in soot."

Mr Preston ran to get a torch to try to see inside the house, while another neighbour stayed with the injured man, who is believed to have lived with the woman. Nothing could be done to save the woman as the smoke and flames were too thick.

Detective Senior Sergeant Kim Libby said the man was now in Middlemore Hospital in an induced coma.

Police have not yet been able to speak to him and are still trying to locate the woman's relatives, who are believed to live overseas.

Officers are not seeking anyone else in connection with her death.

Mr Libby said a post-mortem examination was completed yesterday but police are not revealing the cause of death at this stage - besides saying it was violent.

"The autopsy findings and ongoing inquiries by police reveal that the deceased suffered a violent death," he said.

Last night, neighbours were surprised by news of the murder inquiry, especially as there had been no signs of problems at the house.

Mr Preston said the injured man had seemed genuinely concerned about the woman's still being in the house during the fire.

"He seemed genuine to me when he was saying, 'I couldn't get to her'. He seemed to be in a lot of grief."

Mr Preston said he had seen the man in the driveway they shared with several neighbours but didn't know him well. In the year or so the man and woman had lived in the rental home there hadn't been any obvious problems and he hadn't heard any screaming or shouting.

Another neighbour said the only time he had heard from the couple was when they put a courtesy notice in neighbours' letterboxes saying they were planning a party.

Fire Safety Officer Ray Coleman, who has been at the scene since Sunday, said it was too early to know what caused the fire and he expected it would take at least another day at the house before the scene examination was completed.

A cordon around the scene was expected to remain in place until the examination was finished.