The blaze broke out in an old hall at the rear of the St John’s Orphanage, within the property, just before 5.30pm.

A neighbour told The Post she saw two teenage girls running from the building, wearing backpacks, at about 5.20pm. At that stage she didn’t realise a fire was burning.

Five minutes later she noticed the structure was “well alight.”

Police won’t comment directly on this.

“We are aware the location is used regularly by squatters and young people and this is a line of inquiry,” Detective Inspector Chad Gillies said.

“...We are treating the fire as suspicious until we know otherwise.”

Forensic officers investigated on Tuesday, while general duties police canvassed neighbours. Police are appealing to the public for further information.

Electricity and gas was not extended to the property, NSW Fire and Rescue confirmed.

It’s the second outbreak at the old orphanage in one year. Last November fire destroyed the upper section of the main 1912 building but crews managed to save the old hall at the rear. 

No one was charged over that blaze, though police said it was suspicious.

The historic orphanage has attracted criticism for its state of disrepair and calls for the council to act.

The neighbour said it was not unusual to see squatters and others around the property.

“There were people on the roof a couple of weeks ago and they were smashing windows,” she said.

“You see it all the time.”'

She told The Post the premises was piled high with furniture, newspapers and other material but NSW Fire and Rescue Goulburn station officer Darrell Law said the fuel load was not “excessive.”

Units fully extinguished the blaze by 8.30pm. They had to fight the fire from outside, given the risk of interior structural collapse.

Firefighters managed to save this detached structure last November. The hall was built in 1932 and extended in 1952, a 2003 heritage study by Eric Martens and Associates stated.

Owner John Ferrara had redevelopment plans for the building.

Station officer Law said there were already cracks in the property but they had expanded with the fire.

He speculated the roof at least would have to be replaced.