Hamilton Senior Station Officer Darren Bowler said two adults and two children were taken to hospital suffering smoke inhalation.
He said en route to the fire they spied a "plume of smoke" in the distance. There were also reports of people inside.
They arrived to find the house well involved in flames and the four occupants outside.
He said it was a rapidly developing fire but was brought under control soon after thanks to the 17 firefighters and operational support crew.
It appeared the fire started in a bedroom.
He said the fire proved the importance of working smoke alarms as it appeared the home was not equipped with any.
Bowler reminded people to get out of their house as soon as possible and call 111.
The fire has damaged about 70 per cent of the house.
A St John spokesperson person confirmed four patients were transported to Waikato Hospital in a moderate condition.
Police are at the scene and there is a cordon in place and Newcastle Rd and Dinsdale Rd remain blocked off.
