A couple were home and heard glass breaking from a fire that quickly engulfed their entire home, a witness to the devastating blaze says.

Fire engines are on the scene of a significant house fire at a property on State Highway 1 north of Kaiwaka.

Michelle Miller was driving back to Auckland when she saw the thick black smoke and pulled over, calling 111.

"All I could see was just a whole lot of flames. The whole place was engulfed.

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"I thought it was a bush fire, but it was actually a house fire.

"There must be two houses on the dwelling, and I think it's the back one that's totally burnt down and the one in the front has caught fire a bit as well."

Miller said she talked to a couple, who she thought were aged in their 60s or 70s, who lived in the house and were home when the fire broke out. They were unhurt but deeply shocked.

"All they heard was glass breaking, and next minute the back of the house was totally engulfed. They got out safely.

"The neighbours heard the roosters - they have all been burnt down and everything. It is absolutely devastating."

Miller said she gave the couple the $80 she had in her wallet and was keen to set up a fundraising effort for them.

Crews from Maungaturoto Fire Brigade were among the first to respond.