'No clue': Sydney home destroyed by fire while owner made trip to Bunnings

A homeowner has said he's got "no clue" how a massive fire started at his northern Sydney house, causing the roof to collapse.

Firefighters rushed to the home on Ida Street in Putney at 10.30am after reports of a fire quickly burning through the property.

Owner John Leith has been living at the property for 40-odd years.

READ MORE: Nearly $18 billion in lost or unclaimed super, tax office says

He said he had ducked out to Bunnings when he got a call from his neighbour that his house was on fire.

"I don't have a clue [how it started], I didn't even turn the toaster on, didn't turn the kettle on, all I did in the kitchen was check the mouse trap and then went to Bunnings," he told media from outside his burning home.

"I just couldn't really believe it, you know, it's just something that you would think 'it wouldn't happen to me."

Six trucks faced the ferocious blaze that was threatening neighbouring homes, Ray Buchanan from Fire and Rescue NSW said.

READ MORE: The ASX now predicts four interest rate cuts in 12 months - what does that mean for homeowners?

"We commenced operations for 45 mins to protect neighbouring houses ... either side of the main residence were both under threat,"  Buchanan said.

"There was a significant amount of flame and a high fuel load at the residence [it] took firefighters quite a while to contain it.

"The fire itself was so fierce, and the fuel load [was] so extreme that we were only able to extinguish it externally."

It took firefighters three hours to control the blaze.

Firefighters have not been able to enter the property as the flames caused the roof to collapse, compromising the buildings structral integrity.

READ MORE: Local police constables save dogs from massive industrial fire in Mount Isa

Neighbours told 9News that there were concerns of hoarding at the property for a while.

Investigations into the cause of the fire is now underway.