Police are treating the death of a Tirau grandmother in a house fire as homicide.

Nearly two months after Roma Midwood's body was found inside her home police have announced that the fire was deliberately lit.

This morning Waikato Detective Senior Sergeant Matt Cranshaw said her violent death was shocking, and her family was devastated.

Midwood was found inside her badly damaged Little St home after fire raced through the property in the early hours of May 1.

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At the time police treated her death as suspicious.

Neighbours reported hearing thumping noises and seeing two men leaving the property before the house erupted into flames.

At least one of the men was seen leaving the quiet residential street in a silver car similar to a Nissan Pulsar.

Efforts were made to get the 58-year-old, who lived alone, out of her home but fierce flames prevented anyone getting inside the wooden house.

Anyone with information is asked to phone 0800 766 211 to speak with a member of the inquiry team.

"Roma was a mother, grandmother and loved by those who knew her," said Cranshaw.

Police appealed for information from people out and about or travelling through Tirau in the early hours of May 1.

Cranshaw said investigations were focusing on a silver four-door sedan seen leaving the scene as the blaze took hold.

"It is important that those responsible are held accountable. Someone in the community will know what occurred in the house and the circumstances that led to Roma's death," said Cranshaw.