UPDATE 9.10pm: Jill Russell, 79, lives on Tamure Place and got a terrible fright when she heard "a huge bang from about a mile away".
She ran outside and saw flames shooting through the roof.
Mrs Russell saw a young woman outside the house with severe burns to her face and her clothes torn.
She said ambulances and fire trucks arrived within five or six minutes.
She helped the young woman, who she said had just arrived home from work and opened the door when the house exploded.
The young woman was taken to Whangarei Hospital in a serious condition, and is being transfered to Middlemore Burns Unit.
"It was terrible," Mrs Russell said, "but when you are 79 years old you've seen a lot and you can handle these things. There are quite a few upset people tonight, I am sure."
8.30pm: There have been reports of an explosion in a house on Tamure Place in Ruakaka, about 8pm.
Margaret Hicks, Ruakaka resident, described the house as being empty for months. She said someone had been seen in the house this morning.
Mrs Hicks said she could see thick black smoke in the air, and described huge flames leaping into the air.
She said it sounded like a glass explosion when it happened.
Fire communications shift manager Dallas Ramsay said there were numerous calls about the explosion just after 8pm.
"Multiple houses were reportedly rocked by the explosion."
"We had one caller saying they saw one person severly burnt." That person was transported to hospital by ambulance. There were four trucks still at the scene at 9pm.
The fire is believed to have been caused by a fault in the home's fireplace.