He then searched the house and found the boy's grandmother asleep on a couch.
He helped her outside, and then put out the pot fire.
If he had arrived five minutes later, the house could have been on fire, Mr Mackintosh said.
"It was just pure luck that I arrived when I did. Thankfully no-one was harmed and the only damage was a bit of smoke throughout the house," he said.
Tairawhiti Area Commander Inspector Sam Aberahama praised the constable's quick thinking, saying it probably saved the woman's life.
"This was fantastic work by Ants and is a great example of how diverse our job is.
"Our aim is to keep the community safe and Ants has gone the extra mile to do this. We are very proud of him."
The boy's grandmother did not suffer any injuries.