A dog also died in the blaze, police said.
Emergency services were called to the property in Lanyon Place, in the suburb of Whitby, about 2.20am today.
A neighbour told RNZ the occupants were from a tight-knit family who had lived in the area for years and were lovely, private people.
Another neighbour said an elderly couple lived in the house.
One had just retired and the other had a recent battle with cancer.
Eight fire crews fought the blaze. They remained at the scene this morning dampening down hot spots at the now unstable house.
Fire and Emergency investigators and police will carry out a scene examination to determine the cause of the blaze.
Police were providing support to the family of those involved.