Police and fire safety investigators will be examining three houses in the upper North Island after suspicious fires overnight.
The first was in the Auckland suburb of Mt Wellington at 8.30pm on Thursday after a domestic incident at the property.
A man was taken to hospital in a serious condition as a result of the blaze.
The Fire Service says he was suffering from smoke inhalation and burns.
In Matauri Bay in Northland a man was taken to hospital with serious burns after a fire destroyed half his house just after midnight.
And in Clevedon Park in South Auckland an unoccupied house was well alight when firefighters arrived just before 4am.