A council spokesperson said that the investigations would also determine what could be salvaged from the burnt-out remains of the heritage-listed building, in addition to the feasibility of a total rebuild.

Fortunately, the spokesperson said, there was no-one inside the building. The building was fully insured, and there are no suspicious circumstances surrounding the fire.

Twelve Fire and Rescue NSW trucks attended the blaze, which was believed to have been sparked by an electrical fault in the roof cavity at around 5.30pm.

"Following thorough investigations on Wednesday, Fire and Rescue NSW believe the fire may have started in the roof of the building, however, they have advised the cause of the fire was 'undetermined' due to the scale of damage to the roof."

Lake Macquarie Council purchased the property in 1993, and had used the iconic building as the city's art gallery from 1996 to 2000. "Since then, the house has been leased to an operator who runs the on-site cafe and restaurant," the council spokesperson said.

"The art gallery was closed at the time of the fire as works are underway to expand this facility. The gallery was unaffected by the fire, and is expected to reopen later in the year as planned."

Awaba House has had a colourful history, with three houses built on the Booragul site in more than 130 years. The first house, built in 1878, was destroyed in a house fire in 1886. Unfortunately, the house's occupant Margaret Quigley received severe burns whilst attempting to rescue family valuables, and subsequently died of her injuries.

A second house was built on the site in 1887, however, it fell into disrepair in the 1920s and was demolished in 1927 to make way for a much grander residence. It had been used as a weddings and events venue.

The council spokesperson said that the operator was working with customers who had advanced bookings at Awaba House to help them secure alternate locations in the Lake region.