Update: Investigators continue to probe Kirrawee self-storage building fire

Furniture, vehicles, caravans, boats and other goods with a combined value of millions of dollars were in a self-storage building at Kirrawee, which was severely damaged by fire on Friday night.

A ferocious blaze broke out on the top level of the two-storey iSpace facility in The Boulevarde, but firefighters were able to stop the fire reaching units on the ground level as well as adjoining buildings.

On Monday, Fire and Rescue NSW and police investigators were continuing to probe the cause of the fire.

"The risk of collapse has slowed the investigation, which is common for this type of fire," said Superintendent Adam Dewberry, of Fire and Rescue NSW.

The 63 units in the building are strata titled.

Daniel Astey, of Commercial Property Group, which sold and manages 15-20 units, said they were "generally used to store vehicles, boats, caravans, personal belongings and commercial and building equipment".

Mr Astey said he had "heard a lot of different stories about how the fire started".

The fire started about 8pm, and Fire and Rescue NSW fought it throughout the night, with firefighters in three aerial platforms pouring water through the top of the building after the roof collapsed.

Twelve fire trucks, some from distant parts of Sydney, also attended.

Caleb Miller, who lives nearby in Bath Road and investigated the cause of heavy smoke in the area, said orange flames were coming from the doorways of the building when he arrived,

Mr Miller said he saw a man "running up and down the driveway".

"Someone told me he was working in a unit and left a heat lamp on while he went away for a short time, and his dog, who stayed there, may have knocked it over," Mr Miller said.

Mr Miller, whose employer rents a storage unit in the building, said valuable Ducati motorcycles and a HMV Holden Commodore were among goods stored on the top level.

Fire and Rescue NSW acting superintendent John Moore said on Saturday morning the cause and point of origin of the fire were undetermined.

Mr Moore said he had heard reports a man and his dog had self evacuated.

No injuries were reported, but paramedics assessed a woman who was affected by smoke.