"There was in excess of 20 plants."
Police found large grow lights, fans, a big air vent, buckets, multi boxes and hydroponic equipment inside the home.
"It's probably a step above personal use."
He said police would be talking to the sole male occupant, who was not home at the time, to confirm the purpose of the operation.
Masterton fire officer in charge Kevin Smith said it was lucky the fire was discovered early on, because the house was close to going up in flames.
Arriving at the house, he said, he saw smoke billowing from one end of the building and flames coming out a window.
Firefighters had the fire under control within minutes, he said.
Electrician Craig Hintz, who was installing smart-meters near the property, made the 111 call.
He said at first he thought the smoke was coming from a chimney.
"I actually went up the wrong driveway and when I came back down, the windows were popping.
"Smoke was coming out from under the eaves.
"Waiting for the firecrew out on the road, I could still hear them [windows] pop."
No one was home but a dog was chained up outside.
Police spoke to the home owners' son, who arrived at the house as the fire was being put out.
Mr Irving said the man did not live there but was in charge of leasing it.
The man left with the occupant's dog.
