Northern principal rural fire officer Myles Taylor said the blaze was being treated as suspicious because there was no obvious cause such as a rubbish fire. Police and fire investigators were due to start searching for evidence today.
"We're really pleased the guys managed to keep it to 3-4ha.
"We were very concerned about the house and if it had jumped the creek and gone up the hill we'd be dealing with a much bigger fire," he said.
Just over 24 hours earlier the Rural Fire Authority, worried about the continuing dry weather and soaring fire risk, declared a restricted fire season in the Far North.
That means a permit is required for all outdoor fires except hangi and gas barbecues. Hours before yesterday's fire, Mr Taylor told the Advocate the authority would take a hard line with fire starters by charging them full fire suppression costs, even for fires which were not out of control. A major fire can cost tens or even hundreds of thousands of dollars to put out.
The home most at risk yesterday is being renovated by a family trust.
One of the trustees, who did not want to be named, said a neighbour on the other side of Mangakahia Rd was the first to raise the alarm.
He believed the fire had started in vegetation near a bend in the road.
Rural firefighters were expected to remain overnight to guard against flare-ups and to return today to continue dampening down.
About 2pm on Sunday, Paihia firefighters put out a blaze in long grass at Waterview Place, Haruru Falls, before it could spread into nearby bush.
Kawakawa police Sergeant Kevin Milne said the incident showed how quickly a grass fire could burn out of control in the current conditions.
Two boys at a nearby address, who admitted "fooling around" and lighting a fire in the grass, had been referred to the police Youth Aid section.
About 9.15pm that evening vigilant neighbours using shovels and a fish bin to carry water put out a fire which damaged a house on State Highway 10 east of Awanui.
Damage to the Kareponia home, which is being renovated by an elderly Whangarei couple, was limited largely to the area around the front door. Fire investigator Gary Beer believed the fire had started in a wheelie bin and had little doubt it had been deliberately lit.
Detective Sergeant Trevor Beatson said: "The neighbours certainly did a good job. By all accounts it looked pretty hopeless when they began fighting the fire, but they stuck at it and prevented a lot more damage being done."