UPDATED 12.20PM: The house where the fatal Porirua siege began has gone up in flames, in what's thought to be arson.

The house on Kokiri Crescent is where Pita Te Kira shot and killed police dog Gazza, before fleeing down the street and holing up in a nearby house for nearly 23 hours.

A scene guard is in place and our reporter there says there's a thick smell of smoke in the air.

One of the houses at the centre of the Porirua siege has been severely damaged by a fire @NewstalkZBWgtn pic.twitter.com/uFdoigMp5o

— Georgia Nelson (@georgianelson21) May 1, 2016

The house, half of a semi-detached two-storey unit, appears completely gutted.

The front windows are smashed, the white weatherboards are charred black, the guttering is melted and most of the window frames are burnt.

Twelve-year-old Joyana Poti lives next door and says the fire was terrifying.

"My uncle was saying that when he woke up he had just seen orange, so he went to go wake up my nan, they both came and woke me up."

"I was really scared...really scared."

Police and fire investigators are expected on site later this morning.

The property will likely be demolished due to the damage.

Housing NZ area manager Kathy Furfie says the property is tenanted but the tenant has been staying with family and was not at home when the fire broke out.

She says they'll be working with the tenants make sure they have accommodation while police and fire investigate.