Detective Neville Aiken, of Dunedin, said the Fire Service was alerted to the fire about 4.30am.
None of the people who lived in the house was at home when the fire broke out, but a dog that sought shelter under furniture was killed.
Police understood a bottle was thrown through a bedroom window at the house about 3am, after which the house's occupants left to go elsewhere.
The fire started in the lounge, but the investigation into what caused it was continuing, Det Aiken said.